Catalyst systems for the catalytic oligomerization of olefinic monomers

ABSTRACT

The present invention relates to a ligand and its use in a catalyst for the oligomerization of olefinic monomers, the ligand having the general formula (VI);
 
(R 9 )(R 10 )P—N(R 3 )—P(R 4 )  (VI)
 
wherein:
 
the R 9  and R 10  groups are independently selected from optionally substituted alkyl or heteroalkyl groups; the R 3  group is selected from hydrogen, a hydrocarbyl group, a substituted hydrocarbyl group, a heterohydrocarbyl group, a substituted heterohydrocarbyl group, a silyl group or derivative thereof; the R4 group is an optionally substituted alkylenedioxy, alkylenedimercapto or alkylenediamino structure which is bound to the phosphorus atom through the two oxygen, sulphur or nitrogen atoms of the alkylenedioxy, alkylenedimercapto or alkylenediamino structure or an optionally substituted arylenedioxy, arylenedimercapto or arylenediamino structure which is bound to the phosphorus atom through the two oxygen, sulphur or nitrogen atoms of the arylenedioxy, arylenedimercapto or arylenediamino structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 13/204,020filed Aug. 5, 2011, which is a divisional of U.S. application Ser. No.12/859,337 filed Aug. 19, 2010, which is a divisional of U.S.application Ser. No. 11/961,638 filed Dec. 20, 2007, now U.S. Pat. No.7,803,886, which claims priority to European Application No. 06256571.8filed Dec. 22, 2006, which are all incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to catalyst systems which are useful inthe oligomerization of olefinic monomers.

BACKGROUND OF THE INVENTION

The efficient catalytic trimerization or tetramerization of olefinicmonomers, such as the trimerization and tetramerization of ethylene to1-hexene and 1-octene, is an area of great interest for the productionof olefinic trimers and tetramers of varying degrees of commercialvalue. In particular, 1-hexene is a valuable comonomer for linearlow-density polyethylene (LLDPE) and 1-octene is valuable as a chemicalintermediate in the production of plasticizer alcohols, fatty acids,detergent alcohol and lubrication oil additives as well as a valuablecomonomer in the production of polymers such as polyethylene. 1-Hexeneand 1-octene can be produced by a conventional transition metaloligomerization process, although the trimerization and tetramerizationroutes are preferred.

Several different catalytic systems have been disclosed in the art forthe trimerization of ethylene to 1-hexene. A number of these catalystsare based on chromium.

U.S. Pat. No. 5,198,563 (Phillips) discloses chromium-based catalystscontaining monodentate amine ligands useful for trimerizing olefins.

U.S. Pat. No. 5,968,866 (Phillips) discloses an ethyleneoligomerization/trimerization process which uses a catalyst comprising achromium complex which contains a coordinating asymmetric tridentatephosphane, arsane or stibane ligand and an aluminoxane to producealpha-olefins which are enriched in 1-hexene.

U.S. Pat. No. 5,523,507 (Phillips) discloses a catalyst based on achromium source, a 2,5-dimethylpyrrole ligand and an alkyl aluminiumactivator for use in the trimerization of ethylene to 1-hexene.

Chem. Commun., 2002, 8, 858-859 (BP), discloses chromium complexes ofligands of the type Ar₂PN(Me)PAr₂ (Ar=ortho-methoxy-substituted arylgroup) as catalysts for the trimerization of ethylene.

U.S. Pat. No. 7,141,633 (BP) discloses a catalyst for the trimerizationof olefins comprising a source of chromium, molybdenum or tungsten, aligand containing at least one phosphorus, arsenic or antimony atombound to at least one hydrocarbyl or heterohydrocarbyl group having apolar substituent, but excluding the case where all such polarsubstituents are phosphane, arsane or stibane groups, and optionally anactivator. The ligand used in most of the examples is(2-methoxyphenyl)₂PN(Me)P(2-methoxyphenyl)₂.

Although the catalysts disclosed in the BP documents mentioned abovehave good selectivity for 1-hexene within the C₆ fraction, a relativelyhigh level of products other than the commercially desirable 1-hexeneand 1-octene is typically observed.

U.S. Pat. No. 7,273,959 (Shell) discloses a trimerization catalystcomposition and a process for the trimerization of olefinic monomersusing said catalyst composition.

Catalytic systems for the tetramerization of ethylene to 1-octene haverecently been described. A number of these catalysts are based onchromium.

U.S. Published Patent Applications Nos. 2006/0128910, 2006/0173226,2006/0211903, and 2006/0229480 (Sasol) disclose catalyst compositionsand processes for the tetramerization of olefins. The catalystcompositions disclosed comprise a transition metal and a heteroatomicligand having the general formula (R)_(n)A-B—C(R)_(m) where A and C areindependently selected from a group which comprises phosphorus, arsenic,antimony, oxygen, bismuth, sulphur, selenium, and nitrogen, and B is alinking group between A and C, and R is independently selected from anyhomo or heterohydrocarbyl group of which at least one R group issubstituted with a polar substituent and n and m are determined by therespective valence and oxidation state of A and/or C. The other catalystcompositions disclosed comprise a transition metal and a heteroatomicligand having the general formula (R′)_(n)A-B—C(R′)_(m) where A, B, C, nand m are as defined above, and R′ is independently selected from anyhomo or heterohydrocarbyl group.

U.S. Published Patent Application No. 2006/0128910 (Sasol) discloses thetandem tetramerization and polymerisation of ethylene. Specifically, itdiscloses a process for polymerising olefins to produce branchedpolyolefins in the presence of a distinct polymerization catalyst and adistinct tetramerization catalyst, wherein the tetramerization catalystproduces 1-octene in a selectivity greater than 30% and the 1-octeneproduced is at least partially incorporated into the polyolefin chain.

Although the tetramerization catalysts disclosed in the Sasol documentsmentioned above have good selectivity for 1-octene within the C₈fraction, however, only about 70 to 80% wt. of the C₆ composition is1-hexene, with the remaining C₆ by-product comprising compounds such asmethylcyclopentane and methylenecyclopentane. The presence of theseother C₆ compositions, which have very little commercial use or value,is highly undesirable from both an economic point of view as well asfrom a product separation point of view.

Heteroatom Chemistry, volume 2, page 477 discloses the preparation of(phenyl)₂P—N(isopropyl)-P=catechol andcatechol=P—N(isopropyl)-P=catechol. However there is no disclosure inthis document of the use of these compounds in catalyst systems for thetrimerization and tetramerization of olefins.

It has now surprisingly been found that the catalyst systems derivedfrom the ligands of the present invention are valuable in providing highlevels of both hexene and octene in a process for the simultaneoustrimerization and tetramerization of ethylene, with a high selectivityfor both 1-hexene and 1-octene within the C6 and C8 fractions,respectively. In addition, the catalyst systems of the present inventionhave improved activity and allow the trimerization/tetramerizationreaction to proceed at industrially attractive process conditions (e.g.elevated temperature and pressure) without fast decay of the catalyst.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided aligand having the general formula (I);P(R⁴)—P(R¹)(R²)═N(R³)  (I)wherein:the R¹ group is selected from a hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl and substituted heterohydrocarbyl group;the R² group is selected from hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl and substituted heterohydrocarbyl groups;the R³ is selected from hydrogen, a hydrocarbyl group, a substitutedhydrocarbyl group, a heterohydrocarbyl group, a substitutedheterohydrocarbyl group, a silyl group or derivative thereof;the R⁴ group is an optionally substituted alkylenedioxy,alkylenedimercapto or alkylenediamino structure which is bound to thephosphorus atom through the two oxygen, sulphur or nitrogen atoms of thealkylenedioxy, alkylenedimercapto or alkylenediamino structure or anoptionally substituted arylenedioxy, arylenedimercapto or arylenediaminostructure which is bound to the phosphorus atom through the two oxygen,sulphur or nitrogen atoms of the arylenedioxy, arylenedimercapto orarylenediamino structure.

According to a second aspect of the present invention there is provideda ligand having the general formula (II);P(R¹)(R²)—P(R⁴)═N(R³)  (II)wherein:the R¹ group is selected from a hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl and substituted heterohydrocarbyl group;the R² group is selected from a hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl and substituted heterohydrocarbyl group;the R³ group is selected from hydrogen, a hydrocarbyl group, asubstituted hydrocarbyl group, a heterohydrocarbyl group, a substitutedheterohydrocarbyl group, a silyl group or derivative thereof;the R⁴ group is an optionally substituted alkylenedioxy,alkylenedimercapto or alkylenediamino structure which is bound to thephosphorus atom through the two oxygen, sulphur or nitrogen atoms of thealkylenedioxy, alkylenedimercapto or alkylenediamino structure or anoptionally substituted arylenedioxy, arylenedimercapto or arylenediaminostructure which is bound to the phosphorus atom through the two oxygen,sulphur or nitrogen atoms of the arylenedioxy, arylenedimercapto orarylenediamino structure.

According to a further aspect of the present invention there is provideda process for the preparation of a ligand of formula (I) or (II)comprising reacting:

i) a compound having the general formula (III);(R¹)(R²)P—N(R³)—R⁵  (III)wherein:the R¹ group is selected from hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl and substituted heterohydrocarbyl groups;the R² group is selected from hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl and substituted heterohydrocarbyl groups;the R³ group is selected from hydrogen, a hydrocarbyl group, asubstituted hydrocarbyl group, a heterohydrocarbyl group, a substitutedheterohydrocarbyl group, a silyl group or derivative thereof;the R⁵ group is selected from hydrogen and a P(R⁶)(R⁷)-group;the R⁶ and the R⁷ groups are independently selected from hydrocarbyl,substituted hydrocarbyl, heterohydrocarbyl and substitutedheterohydrocarbyl groups; and

ii) a compound of the formula X—P(R⁴), wherein X is a halide and the R⁴group is a group which comprises an optionally substitutedalkylenedioxy, alkylenedimercapto or alkylenediamino structure which isbound to the phosphorus atom through the two oxygen, sulphur or nitrogenatoms of the alkylenedioxy, alkylenedimercapto or alkylenediaminostructure or an optionally substituted arylenedioxy, arylenedimercaptoor arylenediamino structure which is bound to the phosphorus atomthrough the two oxygen, sulphur or nitrogen atoms of the arylenedioxy,arylenedimercapto or arylenediamino structure,

and if the R⁵ group is hydrogen, a HX-acceptor, preferably at atemperature in the range of from −30 to 200° C.

According to yet a further aspect of the present invention there isprovided a ligand system comprising the product formed by reacting

i) a compound having the general formula (III);(R¹)(R²)P—N(R³)—R⁵  (III)wherein:the R¹ group is selected from hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl and substituted heterohydrocarbyl groups;the R² group is selected from hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl and substituted heterohydrocarbyl groups;the R³ group is selected from hydrogen, a hydrocarbyl group, asubstituted hydrocarbyl group, a heterohydrocarbyl group, a substitutedheterohydrocarbyl group, a silyl group or derivative thereof;the R⁵ group is selected from hydrogen and a P(R⁶)(R⁷)-group;the R⁶ and the R⁷ groups are independently selected from hydrocarbyl,substituted hydrocarbyl, heterohydrocarbyl and substitutedheterohydrocarbyl groups; and

ii) a compound of the formula X—P(R⁴), wherein X is a halide and the R⁴group is a group which comprises an optionally substitutedalkylenedioxy, alkylenedimercapto or alkylenediamino structure which isbound to the phosphorus atom through the two oxygen, sulphur or nitrogenatoms of the alkylenedioxy, alkylenedimercapto or alkylenediaminostructure or an optionally substituted arylenedioxy, arylenedimercaptoor arylenediamino structure which is bound to the phosphorus atomthrough the two oxygen, sulphur or nitrogen atoms of the arylenedioxy,arylenedimercapto or arylenediamino structure,

and if the R⁵ group is hydrogen, a HX-acceptor, preferably at atemperature in the range of from −30 to 200° C.

According to a further aspect of the present invention there is provideda ligand having the general formula (IV);(R¹)(R⁸)P—N(R³)—P(R⁴)  (IV)wherein:the R¹ group is selected from a hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl and substituted heterohydrocarbyl group;the R⁸ group is selected from an aromatic or heteroaromatic group whichcomprise at least one polar substituent group, and optionally one ormore non-polar substituent groups;the R³ group is selected from hydrogen, a hydrocarbyl group, asubstituted hydrocarbyl group, a heterohydrocarbyl group, a substitutedheterohydrocarbyl group, a silyl group or derivative thereof;the R⁴ group is an optionally substituted alkylenedioxy,alkylenedimercapto or alkylenediamino structure which is bound to thephosphorus atom through the two oxygen, sulphur or nitrogen atoms of thealkylenedioxy, alkylenedimercapto or alkylenediamino structure or anoptionally substituted arylenedioxy, arylenedimercapto or arylenediaminostructure which is bound to the phosphorus atom through the two oxygen,sulphur or nitrogen atoms of the arylenedioxy, arylenedimercapto orarylenediamino structure.

According to a further aspect of the present invention there is provideda process for the preparation of a ligand of formula (IV) comprisingreacting:

i) a compound having the general formula (V);(R¹)(R⁸)P—N(R³)—R⁵  (V)wherein:the R¹ group is selected from hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl and substituted heterohydrocarbyl groups;the R⁸ group is selected from an aromatic or heteroaromatic group whichcomprise at least one polar substituent group, and optionally one ormore non-polar substituent groups;the R³ is selected from hydrogen, a hydrocarbyl group, a substitutedhydrocarbyl group, a heterohydrocarbyl group, a substitutedheterohydrocarbyl group, a silyl group or derivative thereof;the R⁵ group is selected from hydrogen or a P(R⁶)(R⁷)-group;the R⁶ and the R⁷ groups are independently selected from hydrocarbyl,substituted hydrocarbyl, heterohydrocarbyl and substitutedheterohydrocarbyl groups; and

ii) a compound of the formula X—P(R⁴), wherein X is a halide and the R⁴group is a group which comprises an optionally substitutedalkylenedioxy, alkylenedimercapto or alkylenediamino structure which isbound to the phosphorus atom through the two oxygen, sulphur or nitrogenatoms of the alkylenedioxy, alkylenedimercapto or alkylenediaminostructure or an optionally substituted arylenedioxy, arylenedimercaptoor arylenediamino structure which is bound to the phosphorus atomthrough the two oxygen, sulphur or nitrogen atoms of the arylenedioxy,arylenedimercapto or arylenediamino structure,

and

if the R⁵ group is hydrogen, a HX-acceptor, preferably at a temperaturein the range of from −30 to 200° C.

According to the present invention there is further provided a ligandhaving the general formula (VI);(R⁹)(R¹⁰)P—N(R³)—P(R⁴)  (VI)wherein:the R⁹ and R¹⁰ groups are independently selected from optionallysubstituted alkyl or heteroalkyl groups;the R³ group is selected from hydrogen, a hydrocarbyl group, asubstituted hydrocarbyl group, a heterohydrocarbyl group, a substitutedheterohydrocarbyl group, a silyl group or derivative thereof;the R⁴ group is an optionally substituted alkylenedioxy,alkylenedimercapto or alkylenediamino structure which is bound to thephosphorus atom through the two oxygen, sulphur or nitrogen atoms of thealkylenedioxy, alkylenedimercapto or alkylenediamino structure or anoptionally substituted arylenedioxy, arylenedimercapto or arylenediaminostructure which is bound to the phosphorus atom through the two oxygen,sulphur or nitrogen atoms of the arylenedioxy, arylenedimercapto orarylenediamino structure.

According to yet a further aspect of the present invention there isprovided a process for the preparation of a ligand of general formula(VI) as described above comprising reacting:

i) a compound having the general formula (VII);(R⁹)(R¹⁰)P—N(R³)—R⁵  (VII)wherein:the R⁹ and R¹⁰ groups are independently selected from optionallysubstituted alkyl or heteroalkyl groups;the R³ group is selected from hydrogen, a hydrocarbyl group, asubstituted hydrocarbyl group, a heterohydrocarbyl group, a substitutedheterohydrocarbyl group, a silyl group or derivative thereof;the R⁵ group is selected from hydrogen or a P(R⁶)(R⁷)-group;the R⁶ and the R⁷ groups are independently selected from hydrocarbyl,substituted hydrocarbyl, heterohydrocarbyl and substitutedheterohydrocarbyl groups; and

ii) a compound of the formula X—P(R⁴), wherein X is a halide and the R⁴group is a group which comprises an optionally substitutedalkylenedioxy, alkylenedimercapto or alkylenediamino structure which isbound to the phosphorus atom through the two oxygen, sulphur or nitrogenatoms of the alkylenedioxy, alkylenedimercapto or alkylenediaminostructure or an optionally substituted arylenedioxy, arylenedimercaptoor arylenediamino structure which is bound to the phosphorus atomthrough the two oxygen, sulphur or nitrogen atoms of the arylenedioxy,arylenedimercapto or arylenediamino structure,

and if the R⁵ group is hydrogen, an HX-acceptor, preferably at atemperature in the range of from −30 to 200° C.

According to a further aspect of the present invention there is provideda catalyst system comprising the product formed by combining:

a) a source of chromium, molybdenum or tungsten;

b) one or more ligands as described herein and;

c) a cocatalyst.

According to a further aspect of the present invention there is provideda catalyst system comprising the product formed by combining:

a) a source of chromium, molybdenum or tungsten;

b) a ligand system as described herein and;

c) a cocatalyst.

According to yet a further aspect of the present invention there isprovided a process for the oligomerisation of olefinic monomers, whereinthe process comprises contacting at least one olefinic monomer with acatalyst system described herein.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “trimerization” means the catalytictrimerization of an olefinic monomer to give a product compositionenriched in the compound derived from the reaction of three of saidolefinic monomers. The term trimerization includes the cases wherein allthe olefinic monomers in the feed stream are identical as well as thecases wherein the feed stream contains two or more different olefinicmonomers.

In particular, the term “trimerization” when used in relation to thetrimerization of ethylene means the trimerization of ethylene to form aC₆ alkene, especially 1-hexene.

The term “trimerization selectivity” when used in relation to thetrimerization of ethylene to 1-hexene means the amount of C₆ fractionformed within the product composition.

The term “1-hexene selectivity” when used in relation to thetrimerization of ethylene to 1-hexene means the amount of 1-hexeneformed within the C₆ fraction of the product composition. The overallyield of 1-hexene in the trimerization of ethylene is the product of the“trimerization selectivity” multiplied by the “1-hexene selectivity”.

The term “tetramerization” means the catalytic tetramerization of anolefinic monomer to give a product composition enriched in the compoundderived from the reaction of four of said olefinic monomers. The termtetramerization includes the cases wherein all the olefinic monomers inthe feed stream are identical as well as the cases wherein the feedstream contains two or more different olefinic monomers.

In particularly, the term “tetramerization” when used in relation to thetetramerization of ethylene means the tetramerization of ethylene toform a C₈ alkene, especially 1-octene.

The term “tetramerization selectivity” when used in relation to thetetramerization of ethylene to 1-octene means the amount of C₈ fractionformed within the product composition.

The term “1-octene selectivity” when used in relation to thetetramerization of ethylene to 1-octene means the amount of 1-octeneformed within the C₈ fraction of the product composition. The overallyield of 1-octene in the tetramerization of ethylene is the product ofthe “tetramerization selectivity” multiplied by the “1-octeneselectivity”.

One aspect of the present invention relates to ligands having thegeneral formulae (I), (II), (IV) and (VI):P(R⁴)—P(R¹)(R²)═N(R³)  (I)P(R¹)(R²)—P(R⁴)═N(R³)  (II)(R¹)(R⁸)P—N(R³)—P(R⁴)  (IV)(R⁹)(R¹⁰)P—N(R³)—P(R⁴)  (VI)wherein R¹, R², R³, R⁴, R⁸, R⁹ and R¹⁰ are as defined above.

While not wishing to be limited by theory, it is thought that in thepresence of an activated metal component (a), e.g. activated chromium,an equilibrium exists between ligands of the P—P═N type and ligands ofthe P—N—P type. For example:P(R⁴)—P(R¹)(R²)═N(R³)

P(R¹)(R²)—P(R⁴)═N(R³)

(R¹)(R²)P—N(R³)—P(R⁴)

The term “hydrocarbyl” as used herein in relation to the R¹-R¹⁰ groupsrefers to a group only containing carbon and hydrogen atoms. Thehydrocarbyl group may be a saturated or unsaturated, linear, branched orcyclic. If the hydrocarbyl is cyclic, the cyclic group may be anaromatic or non-aromatic group. Unless otherwise stated, the preferredhydrocarbyl groups for use herein are those containing from 1 to 20carbon atoms.

The term “substituted hydrocarbyl” as used herein in relation to theR¹-R¹⁰ groups refers to hydrocarbyl groups which are substituted withone or more substituents defined hereinbelow.

The term “heterohydrocarbyl” as used herein refers to a hydrocarbylgroup wherein one or more of the carbon atoms is replaced by aheteroatom, such as Si, S, N or O. Included within this definition areheteraromatic rings, i.e. wherein one or more carbon atom within thering structure of an aromatic ring is replaced by a heteroatom.

The term “substituted heterohydrocarbyl” as used herein refers toheterohydrocarbyl groups which are substituted with one or moresubstituents, defined hereinbelow.

The term “aromatic” as used herein, refers to a monocyclic or polycyclicaromatic ring having from 5 to 14 ring atoms. Examples of polycyclicaromatic groups include biphenyl, binaphthyl, naphthyl and anthracenyl.Unless otherwise stated, the preferred aromatic groups are monocyclic orpolycyclic aromatic rings having from 5 to 10 ring atoms. More preferredaromatic groups are monocyclic aromatic rings containing 6 carbon atoms.A most preferred aromatic group is a phenyl group.

The term “heteroaromatic” as used herein, refers to a monocyclic orpolycyclic, heteroaromatic ring having from 5 to 14 ring atoms,containing from 1 to 3 heteroatoms selected from N, O and S in the ring,with the remaining ring atoms being carbon. Preferably, theheteroaromatic groups are monocyclic heteroaromatic rings, morepreferably monocyclic heteroaromatic groups having from 5 to 10 ringatoms, most preferably from 5 to 6 carbon atoms.

The term “substituted aromatic” as used herein means that the aromaticgroup may be substituted with one or more substituents definedhereinbelow.

The term “substituted heteroaromatic” as used herein means that thearomatic group may be substituted with one or more substituents definedhereinbelow.

Suitable substituent groups for use in the present invention can containcarbon atoms and/or heteroatoms. The substituents may be either polar ornon-polar.

Polar is defined by IUPAC as an entity with a permanent electric dipolemoment. Therefore, as used herein, the term “polar substituent” means asubstituent group which incorporates a permanent electric dipole moment.

IUPAC defines non-polar as an entity without a permanent electric dipolemoment. Therefore, as used herein, the term “non-polar substituent”means a substituent group which does not incorporate a permanentelectric dipole moment.

Suitable substituents include hydrocarbyl and heterohydrocarbyl groups,which may be straight-chain or branched, saturated or unsaturated,aromatic or non-aromatic. Non-limiting examples of suitable aromaticsubstituents include monocyclic and polycyclic aromatic andheteroaromatic groups, preferably aromatic groups having from 5 to 10atoms in the ring, examples of such groups include phenyl and C₁-C₄alkyl substituted phenyl groups. Non-limiting examples of suitablenon-aromatic hydrocarbyl substituents include linear or branched alkylor cycloalkyl groups, preferably having from 1 to 10 carbon atoms, morepreferably 1 to 4 carbon atoms. Non-limiting examples of suitablenon-aromatic heterohydrocarbyl substituents include linear or branchedalkoxy, alkoxyalkyl, alkylsulphonyl, alkylthioalkyl, alkylamino,alkylsilyl and heterocyclic groups.

Other suitable substituent groups include halides such as chloride,bromide and iodide, thiol, —OH, A¹-O—, —S-A¹, —CO-A¹, —NA¹A², —CO—NA¹A²in which A¹ and A², independently, are non-aromatic hydrocarbyl orheterohydrocarbyl groups, preferably having from 1 to 10 carbon atoms,more preferably 1 to 4 carbon atoms, e.g. methyl, ethyl, propyl andisopropyl.

Preferred substituent groups are hydrocarbyl groups, heterohydrocarbylgroups, and halides, in particularly hydrocarbyl groups.

The R¹, R², R⁶ and R⁷ groups are independently selected fromhydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl and substitutedheterohydrocarbyl groups.

Examples of suitable R¹, R², R⁶ and R⁷ groups include optionallysubstituted benzyl, phenyl, tolyl, xylyl, mesityl, biphenyl, naphthyl,anthracenyl, methoxy, ethoxy, phenoxy, tolyloxy, dimethylamino,diethylamino, methylethylamino, thiophenyl, pyridyl, thioethyl,thiophenoxy, trimethylsilyl, dimethylhydrazyl, methyl, ethyl, ethenyl,propyl, butyl, propenyl, propynyl, cyclopentyl, cyclohexyl, ferrocenyland tetrahydrofuranyl groups.

The R¹, R², R⁶ and R⁷ groups are preferably independently selected fromoptionally substituted aromatic and optionally substitutedheteroaromatic groups, more preferably optionally substituted aromaticgroups, especially optionally substituted phenyl.

In one embodiment of the present invention, the R¹ and R² groups areindependently selected from an aromatic or heteroaromatic group,especially phenyl, which comprises at least one polar substituent group,and optionally one or more non-polar substituents.

In another embodiment of the present invention, the R¹ and R² groups areindependently selected from an unsubstituted aromatic or heteroaromaticgroup, preferably an unsubstituted aromatic group, especially phenyl.

In yet another embodiment, R¹ is selected from an aromatic orheteroaromatic group, especially phenyl, which comprises at least onepolar substituent group, and optionally one or more non-polarsubstituents, and R² is selected from an unsubstituted aromatic orheteroaromatic group, especially phenyl.

Suitable non-polar substituent groups include hydrocarbyl substituentgroups which do not contain heteroatoms.

Examples of suitable non-polar substituents include methyl, ethyl,propyl, butyl, isopropyl, isobutyl, tert-butyl, pentyl, hexyl,cyclopentyl, 2-methylcyclohexyl, cyclohexyl, cyclopentadienyl, phenyl,bi-phenyl, naphthyl, tolyl, xylyl, mesityl, ethenyl, propenyl and benzylgroups, or the like.

Preferred non-polar substituent groups include alkyl groups, inparticularly C₁-C₄ alkyl groups such as methyl, ethyl, propyl,isopropyl, butyl, and isobutyl groups.

Suitable polar substituents for use herein include, but are notnecessarily limited to, optionally branched C₁-C₂₀ alkoxy groups, (e.g.connected to the R¹ and R² groups through an oxygen bridging atom);optionally substituted C₅-C₁₄ aryloxy groups, (e.g. connected to the R¹and R² groups through an oxygen bridging atom); optionally branchedC₁-C₂₀ alkoxy(C₁-C₂₀)alkyl groups, (e.g. a C₁-C₂₀ hydrocarbyl groupbearing a C₁-C₂₀ alkoxy group); halides such as chloride, bromide andiodide; hydroxyl; amino; (di-)C₁-C₆ alkylamino; nitro; C₁-C₆alkylsulphonyl; C₁-C₆ alkylthio(C₁-C₆)alkyl groups; sulphate;heterocyclic groups, especially with at least one N and/or O ring atom;and tosyl groups.

Specific examples of suitable polar substituents include methoxy,ethoxy, isopropoxy, phenoxy, pentafluorophenoxy, trimethylsiloxy,dimethylamino, methylsulphonyl, tosyl, methoxymethyl, methylthiomethyl,1,3-oxazolyl, hydroxyl, amino, methoxymethyl, phosphino, arsino,stibino, sulphate, nitro and the like.

Preferably, the polar substituents on the R¹ and R² groups areindependently selected from optionally branched C₁-C₂₀ alkoxy groups,optionally substituted C₅-C₁₄ aryloxy groups, and optionally branchedC₁-C₂₀ alkyl(C₁-C₂₀)alkoxy groups. More preferably, the polarsubstituents are independently selected from optionally branched C₁-C₂₀alkoxy groups, especially optionally branched C₁-C₆ alkoxy groups suchas, for example, methoxy, ethoxy, propoxy, isopropoxy, butoxy,isobutoxy, tert-butoxy, pentoxy, isopentoxy, hexoxy or isohexoxy, ofwhich methoxy, ethoxy and isopropoxy are particularly preferred polarsubstituent groups.

In one embodiment, the R¹ and/or R² groups independently bears a polarsubstituent on at least one of the ortho-positions. Said R¹ and/or R²group can also be optionally substituted by either a polar or non-polargroup at any other position on the aromatic or heteroaromatic group.

For the avoidance of doubt, the phrase “bears a polar substituent on atleast one of the ortho-positions” means, for example, that the R¹ and/orR² group is substituted with a polar substituent on one or both of itsortho positions.

By the term “ortho-position” when used in relation to substituents onthe R¹ and R² groups, it is meant that the substituent is in the orthoposition relative to the atom bonded to the phosphorus atom.

The R³ group is selected from hydrogen, a hydrocarbyl group, asubstituted hydrocarbyl group, a heterohydrocarbyl group, a substitutedheterohydrocarbyl group, a silyl group or derivative thereof. Typically,R³ is selected from hydrogen or the groups consisting of alkyl,substituted alkyl, aryl, substituted aryl, aryloxy, substituted aryloxy,alkenyl, substituted alkenyl, cycloalkyl, substituted cycloalkyl,alkoxycarbonyl, carbonyloxy, alkoxy, aminocarbonyl, carbonylamino,dialkylamino, silyl groups or derivatives thereof, and alkyl or arylgroups substituted with any of these substituents or halogen or a nitrogroup.

Preferably, the R³ group is selected from a hydrocarbyl group, asubstituted hydrocarbyl group, a heterohydrocarbyl group, a substitutedheterohydrocarbyl group, a silyl group or derivative thereof. Morepreferably R³ is an alkyl, substituted alkyl (including heterocyclicsubstituted alkyl with at least one heteroatom, such as N or O, andalkyl groups substituted with a heteroatom or heteroatomic group),cycloalkyl, substituted cycloalkyl, substituted cyclic aryl, substitutedaryl, aryloxy or substituted aryloxy group.

Examples of suitable R³ groups include C₁-C₁₅ alkyl groups, substitutedC₁-C₁₅ alkyl groups, C₁-C₁₅ alkenyl groups, substituted C₁-C₁₅ alkenylgroups, C₃-C₁₅ cycloalkyl groups, substituted C₃-C₁₅ cycloalkyl groups,C₅-C₁₅ aromatic groups, substituted C₅-C₁₅ aromatic groups, C₁-C₁₅alkoxy groups and substituted C₁-C₁₅ alkoxy groups. Most preferred R³groups are the C₁-C₁₅ alkyl groups, which include both linear andbranched alkyl groups; suitable examples include methyl, ethyl, propyl,isopropyl, butyl, isobutyl, tert-butyl, pentyl, alkyl branched pentylgroups, hexyl, alkyl branched hexyl groups, heptyl, alkyl branchedheptyl groups, octyl and alkyl branched octyl groups.

Examples of suitable —N(R³)-groups include —N(methyl)-, —N(ethyl)-,—N(propyl)-, —N(isopropyl)-, —N(butyl)-, —N(t-butyl)-, —N(pentyl)-,—N(hexyl)-, —N(2-ethylhexyl)-, —N(cyclohexyl)-, —N(1-cyclohexylethyl)-,—N(2-methylcyclohexyl)-, —N(benzyl)-, —N(phenyl)-, —N(2-octyl)-,—N(4-methoxyphenyl)-, —N(4-tert-butylphenyl)-, —N((CH₂)₃—N-morpholine)-,—N(Si(CH₃)₃)—, —N(CH₂CH₂CH₂Si(OMe)₃))—, —N(decyl)- and —N(allyl)-.

In the compound of formula X—P(R⁴), the halide group, X, is typicallyselected from fluoride, chloride, bromide or iodide, preferably,fluoride, chloride or bromide, especially bromide or chloride.

The R⁴ group is an optionally substituted alkylenedioxy,alkylenedimercapto or alkylenediamino structure which is bound to thephosphorus atom through the two oxygen, sulphur or nitrogen atoms of thealkylenedioxy, alkylenedimercapto or alkylenediamino structure or anoptionally substituted arylenedioxy, arylenedimercapto or arylenediaminostructure which is bound to the phosphorus atom through the two oxygen,sulphur or nitrogen atoms of the arylenedioxy, arylenedimercapto orarylenediamino structure.

Suitable examples of arylenedioxy groups include, but are not limitedto, 1,2-phenylenedioxy, 1,2-dihydroxynaphthalene,2,3-dihydroxynaphthalene, 1,2-dihydroxyanthracene,1,2-dihydroxyphenanthrene, 2,3-dihydroxyphenanthrene,3,4-dihydroxyphenanthrene, 9,10-dihydroxyphenanthrene,1,8-dihydroxynaphthalene, 2,2′-dihydroxybiphenyl, and2,2′-dihydroxy-1,1′-binaphthyl. The dimercapto and optionallysubstituted diamino analogues of these compounds are examples ofsuitable arylenedimercapto and arylenediamino groups, respectively.

Suitable alkylenedioxy groups include 2,3-dimethyl-2,3-butylenedioxy(=tetramethylethylenedioxy) and 1,3-propylenedioxy. The dimercapto andoptionally substituted diamino analogues of these compounds are examplesof suitable alkylenedimercapto and alkylenediamino groups, respectively.

In preferred embodiments, R⁴ is an optionally substituted alkylenedioxyor arylenedioxy group. 1,2-alkylenedioxy or 1,2-arylenedioxy groups aremost preferred, especially 1,2-arylenedioxy groups.

In a particularly preferred embodiment the R4 group is an optionallysubstituted 1,2-arylenedioxy group having the following structure, whichis bound to the phosphorus atom through the two ortho positioned oxygenatoms of the ortho-arylenedioxy structure, i.e.

wherein the R¹¹ to R¹⁴ groups on the phenyl ring are independentlyselected from hydrogen, hydrocarbyl groups, substituted hydrocarbylgroups, inert functional groups or any two of the R¹¹ to R¹⁴ groups maybe linked together to form a cyclic hydrocarbyl or heterohydrocarbylstructure.

Preferably, the R¹¹ to R¹⁴ groups are independently selected fromhydrogen, halogen, hydrocarbyl, heterohydrocarbyl, or two of the R¹¹ toR¹⁴ groups are linked together to form a cyclic hydrocarbyl orheterohydrocarbyl structure.

Examples of suitable R¹¹ to R¹⁴ groups include hydrogen, fluorine,chlorine, bromine, iodine, C₁-C₁₅ alkyl groups, substituted C₁-C₁₅ alkylgroups, C₁-C₁₅ alkenyl groups, substituted C₁-C₁₅ alkenyl groups, C₃-C₁₅cycloalkyl groups, substituted C₃-C₁₅ cycloalkyl groups, C₅-C₁₅ aromaticgroups, substituted C₅-C₁₅ aromatic groups, C₁-C₁₅ alkoxy groups,substituted C₁-C₁₅ alkoxy groups, alcohol groups, amino groups and thiolgroups. Alternatively, two of the R¹¹ to R¹⁴ groups are linked togetherto form a cyclic hydrocarbyl or heterohydrocarbyl structure, examples ofsuch structures include optionally substituted phenyl, biphenyl,naphthyl, binaphthyl, anthracenyl, phenanthryl, thiophenyl, pyridyl,cyclopentyl, cyclohexyl, ferrocenyl and tetrahydrofuranyl groups.

In one specific preferred embodiment, the R¹¹ to R¹⁴ groups arehydrogen, i.e. ortho-phenylenedioxy.

In the ligand of formula (IV):(R¹)(R⁸)—P—N(R³)—P(R⁴)  (IV)the R¹ group is selected from a hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl and substituted heterohydrocarbyl, as definedhereinabove; andthe R⁸ group is selected from an aromatic or heteroaromatic group whichcomprises at least one polar substituent group, and optionally one ormore non-polar substituent groups.

In the case of ligand (IV), it is preferable that the R¹ group isselected from an optionally substituted aromatic or optionallysubstituted heteroaromatic group, such as an optionally substitutedphenyl, more preferably an optionally substituted aromatic or optionallysubstituted heteroaromatic group which comprises at least one polarsubstituent group, and optionally one or more non-polar substituentgroups, such as a phenyl group substituted with at least one polarsubstituent.

In the case of ligand (IV), it is particularly preferred that R¹ and R⁸are both phenyl groups substituted with a polar group on at least one ofthe ortho positions.

In the case of ligand (VI):(R⁹)(R¹⁰)P—N(R³)—P(R⁴)R⁹ and R¹⁰ are independently selected from optionally substituted alkylor heteroalkyl groups. Suitable alkyl groups include bulky alkyl groupshave 4 or more carbon atoms, preferably alkyl groups having 4 to 8carbon atoms. Suitable heteroalkyl groups include those bulky alkylgroups listed above wherein one or more of the carbon atoms issubstituted with one or more heteroatoms such as Si, S, N or O. Inpreferred embodiments, R⁹ and R¹⁰ are both independently selected froman optionally substituted alkyl, preferably a C4-C8 alkyl, especiallytert-butyl.

The ligands of general formulae (I) and (II) are prepared herein by aprocess which comprises reacting:

i) a compound having the general formula (III):(R¹)(R²)P—N(R³)—R⁵  (III)wherein R¹, R², R³ are as defined above for formulae (I) and (II) and R⁵is selected from hydrogen and a P(R⁶)(R⁷)-group;wherein R⁶ and R⁷ are independently selected from hydrocarbyl,substituted hydrocarbyl, heterohydrocarbyl and substitutedheterohydrocarbyl groups; and

ii) a compound of the formula X—P(R⁴), wherein X is a halide and the R⁴groups is as defined above for ligands of general formulae (I) and (II);preferably at a temperature in the range of from −30 to 200° C.

Importantly, if the R⁵ group is hydrogen, an HX acceptor compound mustalso be used. Suitable HX-acceptors for use herein include neopentyllithium, n-butyl lithium, sec-butyl lithium, lithium hydride, sodiumhydride, potassium hydride, triethylamine, trimethylamine,tripropylamine and the like.

In the case where R⁵ is P(R⁶)(R⁷), it should be noted that the ligandcomposition formed also comprises X—P(R⁶)(R⁷) as by-product. Thisby-product does not interfere to any significant degree with anoligomerization reaction and therefore need not be removed from theresulting ligand composition prior to formation of a catalystcomposition.

In preferred embodiments, R⁶ and R⁷ are selected from an aromatic orheteroaromatic group, preferably an aromatic group comprising at leastone polar substituent group.

The product of the reaction of compound (III) with X—P(R⁴) may comprisea mixture of ligands in equilibrium with each other, for example, amixture of ligands (I) and (II) with their P—N—P analogue(R¹)(R²)P—N(R³)—P(R⁴). Indeed, in the examples section below, thepreparation of ligand F gives a 4:1 mixture of P—P═N and P—N—Pstructures. This mixture of ligands can be used as such in a catalystcomposition, without first separating out the individual ligands. Henceaccording to another aspect of the present invention there is provided aligand system comprising the product formed by reacting (i) a compoundhaving the general formula (III) as defined hereinabove with a compoundof formula X—P(R⁴) as defined hereinabove.

The ligand of general formula (IV) can be prepared by a processcomprising reacting:

(i) a compound having the general formula (V)(R¹)(R⁸)P—N(R³)—R⁵  (V)wherein R¹, R⁸, R³ and R⁵ are as defined hereinabove;and

(ii) a compound of formula X—P(R⁴) wherein X and R⁴ are definedhereinabove;

and if the R⁵ group is H, an HX-acceptor, preferably at a temperature offrom −30° C. to 200° C.

The ligand of formula (VI) can be prepared by a process comprisingreacting:

(i) a compound having the general formula (VII)(R⁹)(R¹⁰)P—N(R³)—R⁵  (VII)wherein R⁹, R¹⁰, R³ and R⁵ are as defined hereinabove; and

(ii) a compound of formula X—P(R⁴) wherein X and R⁴ are definedhereinabove,

and if the R⁵ group is H, an HX-acceptor, preferably at a temperature offrom −30° C. to 200° C.

The ligands and ligand systems of the present invention are useful incatalyst compositions for the oligomerization of olefins. The catalystcompositions of the present invention comprise:

-   -   (a) a source of chromium, molybdenum or tungsten;    -   (b) one or more ligands or ligand systems as described herein;        and    -   (c) a cocatalyst.

The source of chromium, molybdenum or tungsten, component (a), for thecatalyst system of the present invention can include simple inorganicand organic salts of chromium, molybdenum or tungsten. Examples ofsimple inorganic and organic salts are halides, acetylacetonates,carboxylates, oxides, nitrates, sulfates and the like. Further sourcesof chromium, molybdenum or tungsten can also include co-ordination andorganometallic complexes, for example chromium trichloridetris-tetrahydrofuran complex, (benzene)tricarbonylchromium, chromiumhexacarbonyl, and the like. Preferably, the source of chromium,molybdenum or tungsten, component (a), for the catalyst system isselected from simple inorganic and organic salts of chromium, molybdenumor tungsten.

In one embodiment of the present invention, the source of chromium,molybdenum or tungsten, component (a), for the catalyst system is asimple inorganic or organic salt of chromium, molybdenum or tungsten,which is soluble in a solvent such as those disclosed in U.S. Pat. No.7,141,633 which is herein incorporated by reference.

The source of chromium, molybdenum or tungsten can also include amixture of any combination of simple inorganic salts, simple organicsalts, co-ordination complexes and organometallic complexes.

In a preferred embodiment herein, component (a) is a source of chromium,particularly chromium (III).

Preferred sources of chromium for use herein are simple inorganic andorganic salts of chromium and co-ordination or organometallic complexesof chromium. More preferred sources of chromium for use herein are thesimple inorganic and organic salts of chromium, such as salts ofcarboxylic acids, preferably salts of alkanoic acids containing 1 to 30carbon atoms, salts of aliphatic-β-diketones and salts of β-ketoesters(e.g. chromium (III) 2-ethylhexanoate, chromium (III) octanoate andchromium (III) acetylacetonate), and halide salts of chromium, such aschromium trichloride, chromium trichloride tris-tetrahydrofuran complex,chromium tribromide, chromium trifluoride, and chromium tri-iodide.Specific examples of the preferred source of chromium for use herein ischromium (III) acetylacetonate, also called chromiumtris(2,4-pentanedionate), Cr(acac)₃, chromium trichloride, CrCl₃, andchromium trichloride tris-tetrahydrofuran complex, CrCl₃(THF)₃.

The cocatalyst, may in principle be any compound or mixture of compoundsthat generates an active catalyst system with the source of chromium,molybdenum or tungsten, component (a), and the ligand, component (b).

Compounds which are suitable for use as a cocatalyst includeorganoaluminium compounds, organoboron compounds, organic salts, such asmethyllithium and methylmagnesium bromide and the like.

Particularly preferred cocatalysts are organoaluminium compounds.Suitable organoaluminium compounds for use herein are those having theformula AlR¹⁵ ₃, wherein each R¹⁵ group is independently selected fromC₁-C₃₀ alkyl (preferably C₁-C₁₂ alkyl), oxygen containing moieties andhalides, and compounds such as LiAlH₄ and the like. Non-limitingexamples of suitable organoaluminium compounds includetrimethylaluminium (TMA), triethylaluminium (TEA), tri-isobutylaluminium(TIBA), tri-n-octylaluminium, methylaluminium dichloride, ethylaluminiumdichloride, dimethylaluminium chloride, diethylaluminium chloride andaluminoxanes (also called alumoxanes). Mixtures of organoaluminiumcompounds are also suitable for use herein.

In a preferred embodiment herein, the cocatalyst is an aluminoxanecocatalyst. These aluminoxane cocatalysts may comprise any aluminoxanecompound or a mixture of aluminoxane compounds. Aluminoxanes may beprepared by the controlled addition of water to an alkylaluminiumcompound, such as those mentioned above, or are available commercially.In this context it should be noted that the term “aluminoxane” as usedwithin this specification includes commercially available aluminoxanes,which are derived from the corresponding trialkylaluminium by additionof water and which may contain from 2 to 15% wt., typically about 5%wt., but optionally about 10% wt., of aluminium.

Other suitable co-catalysts include those disclosed in U.S. Pat. No.7,141,633, U.S. Published Patent Applications Nos. 2006/0128910,2006/0173226, 2006/0211903, and 2006/0229480, which are incorporatedherein in their entirety by reference.

The components of the catalyst system may be added togethersimultaneously or sequentially in any order so as to provide an activecatalyst. The three catalyst components of the catalyst system, (a), (b)and (c), may be contacted in the presence of any suitable solvent.Suitable solvents are known to those skilled in the art, suitablesolvents may include any inert solvent that does not react with theco-catalyst component, such as saturated aliphatic, unsaturatedaliphatic, aromatic, halogenated hydrocarbons and ionic liquids. Typicalsolvents include, but are not limited to, benzene, toluene, xylene,ethylbenzene, cumene, propane, butane, pentane, heptane, decane,dodecane, tetradecane, methylcyclohexane, methylcycopentane,cyclohexane, 1-hexene, 1-octene and the like. Other examples of suitablesolvents are those disclosed in U.S. Pat. No. 7,141,633, such ashydrocarbon solvents and polar solvents such as diethyl ether,tetrahydrofuran, dichloromethane, chloroform, chlorobenzene and thelike.

The ligand, component (b), can either be formed prior to the formationof the catalyst, can be formed simultaneously with the formation of thecatalyst or a catalyst precursor comprising catalyst components (a) and(b), or can be formed in-situ under an olefinic monomer, e.g. anethylene, atmosphere. If the ligand is formed prior to the formation ofthe catalyst, this is typically performed by reacting the compoundhaving the general formula (III), (V) or (VII) and the compound of theformula X—P(R⁴) in a solvent, such as those mentioned above, at atemperature in the range of from −30 to 200° C. Depending on R⁵═H orR⁵═P(R⁶)(R⁷) temperature is either below 0 and 100° C., respectively.The reaction of the compound having the general formula (III), (V) or(VII) and the compound of the formula X—P(R⁴) can be performed under aninert atmosphere.

Because the by-product formed in the reaction of the compound having thegeneral formula (III), (V) and (VII) and the compound of the formulaX—P(R⁴) does not interfere with the catalytic activity of the catalystcomposition, it is not necessary to isolate the ligand having theformula (I), (II), (IV) and/or (VI). Since the catalytic activity of thecatalyst composition is independent of the presence of the by-productcompound, the optional isolation of the ligand having the formula (I),(II), (IV) or (VI) by any method known in the art, and using saidisolated ligand in the catalyst composition are also included herein. Itis, however, observed that the absence of co-produced (R⁶)(R⁷)P—X e.g.(o-anisyl)₂P—Cl, as in the case of the isolated ligands, leads to higheractivity of the catalyst system as evidenced by the higher TurnoverFrequencies (TOF's). The methods of preparation described hereinabove inwhich the R⁵ group in the compounds of formula (III), (V) or (VII) ishydrogen, advantageously does not produce (R⁶)(R⁷)P—X as byproduct.

In one embodiment of the present invention, the catalyst system isformed by adding the co-catalyst component, (c), to a catalyst precursorcomposition comprising components (a) and (b).

The catalyst system of the present invention may be prepared either inthe presence (i.e. “in-situ”) or absence of the olefinic monomer. Thethree catalyst components of the catalyst system, (a), (b) and (c), maybe combined fully in the absence of the olefinic monomer, or theolefinic monomer may be included prior to contacting the components ofthe catalyst system, simultaneously with the components of the catalystsystem or at any point in the process of contacting the components ofthe catalyst.

The three components of the catalyst system, (a), (b) and (c), ifcomponent (b) has been preformed, may be combined at a temperature inthe range of from −100 to 200° C., preferably 0 to 150° C., morepreferably 20 to 100° C., and, if (b) has not been preformed, may becombined at a temperature in the range of from 30 to 200° C., preferably50 to 150° C., more preferably 70 to 150° C.

The catalyst system of the process of the present invention may beunsupported or supported on a support material. Examples of suitablesupport materials can be found in U.S. Pat. No. 7,141,633 and U.S.Published Patent Applications Nos. 2006/0128910, 2006/0173226,2006/0211903, and 2006/0229480, which are incorporated herein in theirentirety by reference.

The quantity of cocatalyst in the catalyst system the present inventionis typically enough to provide a ratio in the range from 0.1 to 20,000,preferably from 1 to 2000, more preferably 1 to 1000, most preferably 1to 500, aluminium or boron atoms per atom of chromium, molybdenum ortungsten.

The amount of chromium, molybdenum or tungsten, and the amount of theligand, can be present in the catalyst composition in a molar ratio inthe range from 10000:1 to 1:10000, preferably from 100:1 to 1:100, morepreferably from 10:1 to 1:10. Most preferably, the chromium, molybdenumor tungsten, and the ligand are present in a molar ratio in the rangefrom 3:1 to 1:3. Generally the amount of chromium, molybdenum ortungsten, and the amount of ligand are approximately equal or double,i.e. a molar ratio in the range from 1.5:1 to 1:3.

The olefinic monomers suitable for use in the trimerization andtetramerization process of the present invention can be any olefinicmonomers, which can be converted into a trimer or tetramer. Suitableolefinic monomers include, but are not necessarily limited to, ethylene,propylene, optionally branched C₄-C₂₄, preferably C₄-C₂₀ α-olefins,optionally branched C₄-C₂₄, preferably C₄-C₂₀ internal olefins,optionally branched C₄-C₂₄, preferably C₄-C₂₀ vinylidene olefins,optionally branched C₄-C₂₄, preferably C₄-C₂₀ cyclic olefins andoptionally branched C₄-C₂₄, preferably C₄-C₂₀ dienes, as well asoptionally branched C₄-C₂₄, preferably C₄-C₂₀ functionalized olefins.Examples of suitable olefinic monomers include, but are not necessarilylimited to, linear α-olefins, such as ethylene, propylene, 1-butene,1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene,1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene,1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene and 1-eicosene;branched α-olefins such as 4-methylpent-1-ene and 1-ethyl-1-hexene;linear and branched internal-olefins such as 2-butene; styrene;cyclohexene; norbornene and the like.

Mixtures of olefinic monomers can also be used in the process of thepresent invention.

Preferred olefinic monomers for use in the trimerization andtetramerization process of the present invention are propylene andethylene. Especially preferred is ethylene.

The catalyst system and process of the present invention areparticularly useful for the oligomerization of ethylene with a highselectivity towards 1-hexene and 1-octene.

The oligomerization reaction can be performed in solution phase, slurryphase, gas phase or bulk phase.

When the oligomerization is performed in solution or slurry phase, adiluent or solvent, which is substantially inert under theoligomerization conditions may be employed. Suitable diluents orsolvents are aliphatic and aromatic hydrocarbons, halogenatedhydrocarbons and olefins which are substantially inert underoligomerization conditions may be employed, such as those disclosed inU.S. Pat. No. 7,141,633 and U.S. Published Patent Applications Nos.2006/0128910, 2006/0173226, 2006/0211903, and 2006/0229480, which areincorporated herein in their entirety by reference.

The oligomerization process of the present invention may be performed inany one of a number of suitable reactors, which are well known to oneskilled in the art. Typically the oligomerization process of the presentinvention is carried out in a batch, semi-batch or continuous mode.

The oligomerization process of the present invention may be carried outunder the following range of reaction conditions. Typically, thetemperature will be in the range from about 0° C. to about 150° C.,preferably from about 30° C. to about 150° C., and more preferably fromabout 70° C. to about 150° C. The pressure range under which the processof the present invention may be performed is typically in the range offrom below atmospheric pressure to about 100 barg. Preferably, thepressure will be in the range from about 0.1 to about 80 barg, morepreferably from about 0.5 to about 70 barg, especially in the range offrom about 1 to about 60 barg. Temperatures and pressures outside thosestated above may also be employed, however, the reaction product slatewill either have an excess of heavy and/or solid by-products or aninsignificant amount of the trimer or tetramer.

By varying the temperature and pressure it is possible for ratio oftrimers and tetramers produced in the process of the present inventionto be varied. A trend observed indicates that the amount of trimersproduced in the process of the present invention increases withincreasing temperature. Another trend which has been observed indicatesthat the amount of tetramers produced in the process of the presentinvention increases with increasing pressure.

Therefore, by varying the reaction conditions of the process of thepresent invention, the amount of trimers and tetramers in theoligomerization product composition may be varied. This may be usefulfor a continuous or semi-continuous oligomerization process whichproduces a high proportion of trimers and tetramers, wherein the productcomposition can be changed (e.g. from producing a higher proportion oftrimers to a higher proportion of tetramers, or vice-versa,) by changingthe reactor conditions without having to interrupt the olefinic monomerfeed or the oligomerization product flow. In particular, this may beespecially useful for a continuous or semi-continuous process for theoligomerization of ethylene, wherein the product composition can bechanged (e.g. from producing a higher proportion of 1-hexene to a higherproportion of 1-octene, or vice-versa) by changing the reactorconditions without having to interrupt the olefinic monomer feed or theoligomerization product flow.

In one embodiment of the present invention, there is a process for theoligomerization of olefinic monomers, wherein the process comprisescontacting at least one olefinic monomer under oligomerization reactionconditions with a catalyst system of the process of the presentinvention, wherein the process is a continuous or semi-continuousprocess and the reaction conditions are varied during the process.Variation of the reaction conditions can be performed to make continualadjustments to a process to ensure a consistent product composition orcan be performed to a process to change the product compositionproduced. A preferred version of this embodiment is a process for theoligomerization of ethylene, wherein the process comprises contactingethylene with a catalyst system of the process of the present invention,wherein the process is a continuous or semi-continuous process and thereaction conditions are varied during the process.

Separation of the products, reactant and catalyst can be performed byany technique known to one skilled in the art, such as distillation,filtration, centrifugation, liquid/liquid separation, extraction, andthe like.

Further details regarding reactors, solvents, separation techniques, andthe like, can be found in U.S. Pat. No. 7,141,633 which is hereinincorporated by reference.

The use of the process of the present invention for the catalyticoligomerization of olefinic monomers provides a simple method forproducing trimers and tetramers of the olefinic monomer. In particular,the use of the process of the present invention for the catalyticoligomerization of ethylene provides a simplified method for producing1-hexene and 1-octene, with very high selectivity for 1-hexene and1-octene over all the other products formed in the C₆ and C₈ fractionsrespectively.

The overall yield of 1-hexene and 1-octene in the process for thetrimerization and tetramerization of ethylene of the present inventiondepends upon the reaction conditions employed.

Typically, the trimerization and tetramerization selectivity (i.e. theamount of trimers and tetramers of the olefinic monomers in the overallproduct composition) of the process of the present invention is at least60% wt, preferably at least 70% wt, more preferably at least 80% wt, ofthe overall product composition. The trimerization and tetramerizationselectivity for the trimerization and tetramerization of ethylene (i.e.the amount of C₆ and C₈ fraction in the overall product composition)using the process of the present invention is at least 60% wt,preferably at least 70% wt, more preferably at least 80% wt, of theoverall product composition.

The amount of 1-hexene produced by the trimerization and tetramerizationof ethylene using the process of the present invention is typically inthe range of from 10% wt to 90% wt, preferably from 11% wt to 85% wt,more preferably from 12% wt to 80% wt, of the overall productcomposition. The amount of 1-octene produced by the trimerization andtetramerization of ethylene using the process of the present inventionis typically in the range of from 10% wt to 90% wt, preferably from 11%wt to 85% wt, more preferably from 12% wt to 80% wt, of the overallproduct composition.

The 1-hexene selectivity (i.e. the amount of 1-hexene present in the C₆fraction of the product composition) in the trimerization andtetramerization of ethylene using the process of the present inventionis preferably at least 85% wt, more preferably at least 90% wt, mostpreferably at least 92% wt of the C₆ fraction of the productcomposition.

The 1-octene selectivity (i.e. the amount of 1-octene present in the C₈fraction of the product composition) in the trimerization andtetramerization of ethylene using the process of the present inventionis preferably at least 85% wt, more preferably at least 90% wt, mostpreferably at least 92% wt, of the C₈ fraction product composition.

The amount of C₁₀ produced in the trimerization and tetramerization ofethylene using the process of the present invention is typically at mostabout 10% wt.

The amount of solids produced in the trimerization and tetramerizationof ethylene using the process of the present invention is typically atmost about 5% wt. Lower levels of solid olefin waxes and polyethyleneproduced in the trimerization and tetramerization of ethylene aredesirable in commercial operations as this can reduce the amount offouling of the reactor equipment, reduce the amount of waste by-productsand reduce the amount of operational “downtime” due to maintenance andcleaning of the reactor equipment.

In one embodiment of the present invention, the olefinic productcomposition of the oligomerization of ethylene using the process of thepresent invention typically comprises a combined total content of1-hexene and 1-octene in the range of from 60 to 98% wt of the overallproduct composition, preferably from 70 to 98% wt and more preferablyfrom 80 to 100% wt, wherein the 1-hexene content is typically at least10% wt of the overall product composition, the 1-hexene selectivity istypically at least 90% wt of the C₆ fraction of the product composition,the 1-octene content is typically at least 10% wt of the overall productcomposition, the 1-octene selectivity is typically at least 90% wt ofthe C₈ fraction of the product composition, and the amount of solidsproduced is at most about 5% wt of the overall product composition.

In another embodiment of the present invention, the olefinic productcomposition of the trimerization and tetramerization of ethylene usingthe process of the present invention comprises a total content ofcompounds other than 1-hexene and 1-octene of at most 40% wt of theoverall product composition, preferably at most 30% wt and morepreferably at most 20% wt, wherein the 1-hexene content is typically atleast 10% wt of the overall product composition, the 1-hexeneselectivity is typically at least 90% wt of the C₆ fraction of theproduct composition, the 1-octene content is typically at least 10% wtof the overall product composition, the 1-octene selectivity istypically at least 90% wt of the C₈ fraction of the product composition,and the amount of solids produced is at most about 5% wt of the overallproduct composition.

The process of the present invention is illustrated by the followingnon-limiting examples.

EXAMPLES General Procedures and Characterisation

All chemicals used in preparations were purchased from Aldrich and usedwithout further purification unless mentioned otherwise.

All the operations with the catalyst systems were carried out undernitrogen atmosphere. All solvents used were dried using standardprocedures. Anhydrous toluene (99.8% purity) was dried over 4 Åmolecular sieves (final water content of about 3 ppm).

Ethylene (99.5% purity) was purified over a column containing 4 Åmolecular sieves and BTS catalyst (BASF) in order to reduce water andoxygen content to <1 ppm.

The oligomers obtained were characterised by Gas Chromatography (GC), inorder to evaluate oligomer distribution using a HP 5890 series IIapparatus and the following chromatographic conditions:

Column: HP-1 (cross-linked methyl siloxane), film thickness=0.25 μm,internal diameter=0.25 mm, length 60 m (by Hewlett Packard); injectiontemperature: 325° C.; detection temperature: 325° C.; initialtemperature: 40° C. for 10 minutes; temperature programme rate: 10.0°C./minute; final temperature: 325° C. for 41.5 minutes; internalstandard: n-hexylbenzene. The yields of the C₄-C₃₀ olefins were obtainedfrom the GC analysis.

The amount of “solids”, mainly consisting of heavy wax and polyethylene,has been determined by weighing, after its isolation from the reactorwall and appendages, followed by washing with toluene on a glass filter(P3) and by vacuum drying.

The amount of “total product” is the sum of the amount of largelyolefinic product derived from GC analysis and the amount of solids.

The NMR data was obtained at room temperature with a Varian 300 MHz or400 MHz apparatus.

Catalyst Compositions

A number of catalyst systems containing ligand compositions A, A′, B′,C″, C′, C*, D″, D′, E, F, G″, H″, K″, L, M″, N″, Q, T′, U and V and achromium source were prepared and used in the oligomerisation reactionsdescribed below.

Chromium Source

Chromium tris-(2,4-pentanedionate), also called chromiumtris(acetylacetonate), was used as the chromium source throughout.

Ligand Composition A

The reaction product of (2-methoxyphenyl)₂PNH(methyl) and(o-phenylenedioxy)PCl (ligand composition A) was prepared as follows.

Under a nitrogen atmosphere 1.015 g (3.62 mmol) (2-methoxyphenyl)₂PCl(available from Aldrich) was added to 10 ml methylamine (2M in THF) in50 ml pentane. The resulting mixture was stirred overnight at roomtemperature. The precipitate was removed by centrifugation. The solventswere removed from the resulting solution under vacuum. Washing withpentane yielded 0.85 g (3.09 mmol; (84%)) (2-methoxyphenyl)₂PNH(methyl)as a white solid. ³¹P-NMR (in C₆D₆) δ 31.6.

Under a nitrogen atmosphere, 133 mg (1.70 mmol) of neopentyl lithium wasslowly added to 428 mg (1.55 mmol) of (2-methoxyphenyl)₂PNH(methyl) in60 ml dry toluene. To the resulting mixture 280 mg (1.60 mmol)(o-phenylenedioxy)PCl (available from Aldrich) in 5 ml toluene wasslowly added. The mixture was stirred for 2 hours at room temperature.To the mixture 25 ml pentane was added. The precipitate was removed bycentrifugation. The solvent was removed under vacuum. The resultingsticky material was washed with pentane (twice) and a white solid wasisolated. According to ³¹P-NMR the product consisted at leastpredominantly of a P—P═N(methyl) structure with on one P atom theo-phenylenedioxy group and on the other P atom two 2-methoxyphenylgroups (either (o-phenylenedioxy)P(2-methoxyphenyl)₂PN(methyl) or(2-methoxyphenyl)₂P(o-phenylenedioxy)PN(methyl)). ³¹P-NMR (in C₆D₆)signals at δ 153.1 and 35.3 (J_(PP)=359 Hz).

Ligand Composition A′

The reaction product of (2-methoxyphenyl)₂PN(methyl)P(2-methoxyphenyl)₂and (o-phenylenedioxy)PCl (ligand composition A′) was prepared asfollows.

Under a nitrogen atmosphere, 87 mg (o-phenylenedioxy)PCl (available fromAldrich) was added to 260 mg(2-methoxyphenyl)₂PN(methyl)P(2-methoxyphenyl)₂ (Ligand composition K″)in 2 ml dry toluene. The resulting mixture was heated to 110° C.overnight.

The solvent was removed from the solution by heating under vacuum. Partof the resulting mixture was dissolved in pentane, the pentane solutionwas isolated and subsequently the solvent was removed and the residuewas dried under vacuum. According to ³¹P-NMR spectroscopy, the productwas an approximately 1 to 1 (mol/mol) mixture of (2-methoxyphenyl)₂PCland a P—P═N(methyl) structure with on one P atom the o-phenylenedioxygroup and on the other P atom two 2-methoxyphenyl groups (either(o-phenylenedioxy)P(2-methoxyphenyl)₂PN(methyl) or(2-methoxyphenyl)₂P(o-phenylenedioxy)PN(methyl)). ³¹P-NMR (in C₆D₆) δ153.1 and 35.3 (J_(pp)=359 Hz).

This mixture was used as such in the catalyst for ethyleneoligomerization experiments without further purification.

Ligand Composition B′

The reaction product of(2-methoxyphenyl)(phenyl)PN(methyl)P(phenyl)(2-methoxyphenyl) and(o-phenylenedioxy)PCl (ligand composition B′) was prepared as follows.

The (2-methoxyphenyl)(phenyl)PN(CH₃)P(2-methoxyphenyl)(phenyl) ligandwas prepared by first forming a suspension of 0.42 g lithium (60 mmol)in 80 ml of tetrahydrofuran (THF), to which was added 9.66 g of(2-methoxyphenyl)₂P(phenyl) (30 mmol) at 0° C. under an argonatmosphere. The mixture was stirred for 4 hours, after which time a 5 mlaliquot of methanol was added. 60 ml of toluene was added to themixture, after which the solution was extracted with two 40 ml portionsof water. The extracted toluene solution was then concentrated to avolume of approximately 20 ml, which resulted in formation of asuspension. The concentrated toluene solution was filtered, and 4.6 g ofC₂Cl₆ was added to the toluene filtrate, which was then stirred for 2hours at 90° C. The HCl gas, which evolved from the reaction, was“trapped” in an alkali bath. The mixture was then cooled to roomtemperature and purged with nitrogen to remove all of the remaining HClpresent in the solution.

At room temperature, a 5 ml aliquot of triethylamine was added to theconcentrated toluene solution and left for a few minutes, after which 6ml of 2 M H₂NMe (12 mmol) was added a few drops at a time. Thesuspension was filtered and washed with 20 ml of toluene. The toluenefiltrate and the toluene wash fraction were combined. The combinedtoluene fractions were evaporated to dryness and 30 ml of methanol wasadded. The methanol solution was left overnight at −35° C. wherein awhite (2-methoxyphenyl)(phenyl)PN(CH₃)P(2-methoxyphenyl)(phenyl)precipitate was formed in the solution. The precipitated ligand was thenisolated.

The precipitated ligand consisted of two isomers, a racemic isomer (theRR and/or the SS enantiomers of the ligand) and a meso isomer (the RSenantiomer of the ligand). The proportions of these two isomers weredetermined by ³¹P NMR with peaks at 63.18 and 64.8 ppm corresponding tothe two different isomers respectively. These two samples consisted ofmixtures of both the racemic and the meso isomers having weight ratiosof 57/43 and 92/8 respectively. Only the sample of(2-methoxyphenyl)(phenyl)PN(CH₃)P(2-methoxyphenyl)(phenyl) with theracemic and the meso isomers in a weight ratio of 57/43 was used.

Under a nitrogen atmosphere, 14 mg (o-phenylenedioxy)PCl was added to 37mg (2-methoxyphenyl)(phenyl)PN(methyl)P(phenyl)(2-methoxyphenyl) in 1.0ml dry CO₆. The resulting mixture was heated overnight in an oil bath at90° C.

Based on the ³¹P-NMR spectrum, the main products were an approximate 1to 1 (mol/mol) mixture of (2-methoxyphenyl)(phenyl)PCl and aP—P═N(methyl) structure with on one P atom the o-phenylenedioxy groupand on the other P atom one 2-methoxyphenyl group and one phenyl group(either (o-phenylenedioxy)P(2-methoxyphenyl)(phenyl)PN(methyl) or(2-methoxyphenyl)(phenyl)P(o-phenylenedioxy)PN(methyl)). ³¹P-NMR (inC₆D₆) δ 151.7 and 43.0 (J_(pp)=353 Hz).

This mixture was used as such in the catalyst for ethyleneoligomerization experiments without further purification.

Ligand Composition C″, Ligand Composition C′ and Ligand Composition C*

The reaction product of (2-methoxyphenyl)₂PNH(isopropyl) and(o-phenylenedioxy)PCl (ligand composition C″) was prepared as follows.

Under a nitrogen atmosphere, 3 ml triethylamine was added to 1.5 mlisopropylamine (17.6 mmol) in 5 ml dry toluene. To the resultingmixture, 2.2 g (7.84 mmol) (2-methoxyphenyl)₂PCl in 20 ml toluene wasslowly added and allowed to stir overnight at room temperature. Theprecipitate was removed by centrifugation. The solvents were removedfrom the resulting solution in vacuo. Washing with pentane yielded(2-methoxyphenyl)₂PNH(isopropyl) as a white solid. ³¹P-NMR in C₆D₆) δ21.8.

Under a nitrogen atmosphere, 60 mg (0.77 mmol) of neopentyl lithium wasslowly added to 226 mg of (2-methoxyphenyl)₂PNH(isopropyl) in 20 ml drytoluene. To the resulting mixture 130 mg (0.75 mmol)(o-phenylenedioxy)PCl in 1 ml toluene was slowly added. The mixture wasstirred for 2 hours at room temperature. The precipitate was removed bycentrifugation. The solvent was removed in vacuo. After washing withmethanol a product, which according to ³¹P-NMR had at leastpredominantly the P—N(isopropyl)-P structure, i.e.(2-methoxyphenyl)₂PN(isopropyl)P(o-phenylenedioxy), was isolated as awhite solid. ³¹P-NMR (in C₆D₆) δ 156.9 and 11.6 (J_(pp)=−20 Hz).

According to ³¹P-NMR spectroscopy the same P—N—P product as present inligand composition C″,(2-methoxyphenyl)₂PN(isopropyl)P(o-phenylenedioxy), was formed almostquantitatively upon reaction of (o-phenylenedioxy)PCl with ligandcomposition N″, (2-methoxyphenyl)₂PN(isopropyl)P(phenyl)₂ overnight inC₆D₆ at 80° C. with concomitant formation of an equivalent amount of(phenyl)₂PCl (designated ligand composition C′). ³¹P-NMR (in C₆D₆) δ 157and 12.

According to ³¹P-NMR spectroscopy the same P—N—P product as present inligand composition C″,(2-methoxyphenyl)₂PN(isopropyl)P(o-phenylenedioxy), was formed almostquantitatively upon reaction of (o-phenylenedioxy)PCl with P—P═N ligandcomposition L, (2-methoxyphenyl)₂P—P(2-methoxyphenyl)₂═N(isopropyl)during <0.5 hour in C₆D₆ at 20° C. with concomitant formation of anequivalent amount of (2-methoxyphenyl)₂P—Cl (designated ligandcomposition C*). ³¹P-NMR (in C₆D₆) δ 157 and 12.

Ligand Composition D″ and Ligand Composition D′(Comparative)

The (phenyl)₂PN(isopropyl)P(o-phenylenedioxy) ligand composition wasprepared according to the method reported in Heteroatom Chem. Vol. 2,477 (1991).

Under a nitrogen atmosphere, 12 ml triethylamine was added to 3.39 gisopropylamine in 10 ml dry toluene. To the resulting mixture, 5.15 ml(phenyl)₂PCl (available from Aldrich) was slowly added and allowed tostir overnight at room temperature. The precipitate was removed byfiltration. The solvents were removed from the resulting solution invacuo. To the evaporation residue, pentane was added. The solvent wasthen removed in vacuo from the pentane solution, yielding(phenyl)₂PNH(isopropyl) as a colourless oil, which crystallized onstanding at room temperature. ³¹P-NMR (in C₆D₆) δ 35.8.

Under a nitrogen atmosphere, 1.7 ml triethyl amine was added to 2.00 gof (phenyl)₂PNH(isopropyl) in 10 ml dry toluene. The resulting mixturewas cooled to approximately 0° C. and 1.435 g of (o-phenylenedioxy)PCl(available from Aldrich) was slowly added. The mixture was then stirredovernight at room temperature (approximately 20° C.).

The precipitate which formed in the solution was removed bycentrifugation. The resulting solution was concentrated under vacuum andwas subsequently filtered over silica gel.

The solvent was removed under vacuum, which yielded a white solid of(phenyl)₂PN(isopropyl)P(o-phenylenedioxy). ³¹P-NMR (in C₆D₆) δ 157.4 and30.0 (J_(pp)=17 Hz).

According to ³¹P-NMR spectroscopy the same P—N—P product as present inligand composition D″, (phenyl)₂PN(isopropyl)P(o-phenylenedioxy), wasformed in about 10% yield upon reaction of (o-phenylenedioxy)PCl withligand composition M″, (phenyl)₂PN(isopropyl)P(phenyl)₂ overnight inC₆D₆ at 90° C. with concomitant formation of (phenyl)₂PCl (designatedligand composition D′). The remainder of the reaction mixture werepredominantly starting components. ³¹P-NMR (in C₆D₆) δ 157 and 30.

Ligand Composition E

The reaction product of (phenyl)₂PNH(methyl) and (o-phenylenedioxy)PCl(ligand composition E) was prepared as follows.

Under a nitrogen atmosphere, 400 mg triethylamine was added to 2 mlmethylamine (2 M in THF) in 5 ml dry toluene. The resulting solution wascooled to −15° C. and 440 mg (phenyl)₂PCl in 5 ml toluene was slowlyadded and allowed to stir overnight at room temperature. To theresulting mixture pentane was added. The precipitate was removed bycentrifugation. The solvents were removed under vacuum. The resultingsticky product was extracted with cold pentane. After removing thepentane under vacuum (phenyl)₂PNH(methyl) was isolated as an oil.³¹P-NMR (in C₆D₆) δ 45.7.

To 55 mg (phenyl)₂PNH(methyl) in 1 ml C₆D₆ was added 50 mg triethylamineand 44 mg (o-phenylenedioxy)PCl. After standing overnight 2 ml ofpentane was added. The precipitate was removed by centrifugation. Thesolvents were removed under vacuum. The product was isolated as an oil.According to ³¹P-NMR the product consisted at least predominantly of aP—P═N(methyl) structure with on one P atom the o-phenylenedioxy groupand on the other P atom two phenyl groups (either(o-phenylenedioxy)P(phenyl)₂PN(methyl) or(phenyl)₂P(o-phenylenedioxy)PN(methyl)). ³¹P-NMR (in C₆D₆) δ 151.9 and49.1 (J_(pp)=351 Hz).

Ligand Composition F

The reaction product of (tert-butyl)₂PNH(methyl) and(o-phenylenedioxy)PCl (ligand composition F) was prepared as follows.

Under a nitrogen atmosphere, 3 ml triethylamine was added to 6 mlmethylamine (2 M in THF) in 20 ml dry toluene. To the resultingsolution, 1.6 g (tert-butyl)₂PCl (available from Aldrich) was slowlyadded and allowed to stir overnight at room temperature. To theresulting mixture pentane was added. The precipitate was removed bycentrifugation. The solvents were removed under vacuum. The resultingoil was crystallized from pentane (−20° C.). Yielding white crystals of(tert-butyl)₂PNH(methyl). ³¹P-NMR (in C₆D₆) δ 82.8. This product hasbeen described as an oil in Phosphorus, Sulfur and Silicon, 1990, vol.54, p. 55-61.

Under a nitrogen atmosphere, 95 mg triethylamine was added to 83 mg(tert-butyl)₂PNH(methyl) in 3 ml dry toluene. To the resulting solution,83 mg (o-phenylenedioxy)PCl was slowly added and allowed to stirovernight at room temperature. To the resulting mixture pentane wasadded. The precipitate was removed by centrifugation. The solvents wereremoved under vacuum. The resulting white solid was washed with coldpentane. The ³¹P-NMR spectrum in C₆D₆ showed 2 products one with a setof doublets at δ 151.2 and 84.7 (J_(pp)=375) and one with a set ofdoublets at δ 153.8 and 115.8 (J_(pp)=42 Hz) in a 4 to 1 (mol/mol)ratio. Most probably the product consisted of a 4 to 1 (mol/mol) mixtureof isomers having a P—P═N(methyl) structure with on one P atom theo-phenylenedioxy group and on the other P atom two tert-butyl groups(either (o-phenylenedioxy)P(tert-butyl)₂PN(methyl) or(tert-butyl)₂P(o-phenylenedioxy)PN(methyl)) and a P—N(methyl)-Pstructure, (tert-butyl)₂P—N(methyl)-P(o-phenylenedioxy).

Ligand Composition G″

The reaction product of (2-methoxyphenyl)₂PNH(pentafluorophenyl) and(o-phenylenedioxy)PCl (ligand composition G″) was prepared as follows.

Under a nitrogen atmosphere, 0.5 g (6.3 mmol) of neopentyllithium(available from Aldrich) was slowly added to 1.15 g (6.3 mmol)pentafluoroaniline (available from Aldrich) in 25 ml dry toluene andstirred for 0.5 hour at room temperature. To the resulting mixture 1.76g (6.3 mmol) (2-methoxyphenyl)₂PCl in 15 ml toluene was slowly added andallowed to stir for 1 hour at room temperature. The precipitate wasremoved by centrifugation. The solution was concentrated to about 5 ml.Pentane was added (about 20 ml), the precipitate was collected. Washingwith pentane yielded (2-methoxyphenyl)₂PNH(C₆F₅) as a white solid.³¹P-NMR (in C₆D₆) δ 38.4 (t) (J_(PF)=60 Hz). ¹⁹F-NMR (in C₆D₆) δ−156(o); −165.2 (m); −170.3 (p).

Under a nitrogen atmosphere, 128 mg (1.64 mmol) of neopentyllithium wasslowly added to 700 mg (1.64 mmol) (2-methoxyphenyl)₂PNH(C₆F₅) in 25 mldry toluene and stirred for 1 hour at room temperature. To the resultingmixture 286 mg (1.64 mmol) (o-phenylenedioxy)PCl in 10 ml toluene wasslowly added and allowed to stir for 1 hour at room temperature. Theprecipitate was removed by centrifugation. The solvent was removed invacuo. Pentane was added (about 10 ml) yielding a clear solution. Fromthis solution (2-methoxyphenyl)₂PN(C₆F₅)(o-phenylenedioxy) precipitatedin several fractions. ³¹P-NMR (in C₆D₆) δ 138.4 and 51.3 (J_(PP)=16 Hz).¹⁹F-NMR (in C₆D₆) δ−143 (o); −164.1 (m); −157.1 (p).

Ligand Composition H″ (Comparative)

The (o-phenylenedioxy)PN(methyl)P(o-phenylenedioxy) ligand compositionwas prepared by analogy to the method reported for the preparation of(o-phenylenedioxy)PN(isopropyl)P(o-phenylenedioxy) in Heteroatom Chem.Vol. 2, 477 (1991).

Under a nitrogen atmosphere 1 ml methylamine (2 M in THF) was added to 5ml dry toluene. This solution was cooled to −20° C. At this temperatureslowly 150 mg (o-phenylenedioxy)PCl in 1 ml toluene was slowly added.After several days 87 mg Et₃N in 5 ml pentane was added. The precipitatewas removed by centrifugation. The solvents were removed under vacuum.Yielding (o-phenylenedioxy)PNH(methyl) contaminated with a small amountof toluene. ³¹P-NMR (in C₆D₆) δ 143.9.

To 30 mg (o-phenylenedioxy)PNH(methyl) in 1 ml C₆D₆ was added 30 mgtriethylamine and 30 mg (o-phenylenedioxy)PCl. An instantaneous reactionwas observed by ³¹P-NMR. Finally 2 ml of pentane was added. Theprecipitate was removed by centrifugation. The solvents were removedunder vacuum. The final product was isolated as a white solid. ³¹P-NMR(in C₆D₆) δ 142.0.

Ligand Composition K″ (Comparative)

The (2-methoxyphenyl)₂PN(CH₃)P(2-methoxyphenyl)₂ ligand was prepared byfirst forming a solution of 1.59 g (5 mmol) (2-methoxyphenyl)₂PNEt₂ in20 ml diethyl ether. To this solution 10 ml of a 1 M HCl solution indiethyl ether (10 mmol HCl) was added under an inert atmosphere at roomtemperature. The suspension thus formed was stirred overnight. Thediethyl ether was removed from the product under vacuum and 20 ml of drytoluene was added. The resulting solution was filtered and the toluenewas removed from the filtrate under vacuum to yield a white solid(2-methoxyphenyl)₂PCl product.

A solution of 0.51 g (5 mmol) of triethylamine in 20 ml of drydichloromethane was added to the (2-methoxyphenyl)₂PCl product. To theresulting mixture, 1.25 ml of a 2 M H₂NMe solution in THF (2.5 mmol) wasadded and allowed to stir overnight. The solvents were removed from theresulting solution in vacuo and 20 ml of dry toluene was added. Themixture was then filtered.

The toluene was removed from the filtrate under vacuum, and 10 ml ofmethanol was added to the residue to produce a suspension, which wasfiltered once more, to leave the solid white(2-methoxyphenyl)₂PN(CH₃)P(2-methoxyphenyl)₂ product which was isolated.

Ligand Composition L (Comparative)

The reaction product of (2-methoxyphenyl)₂PNH(isopropyl) and(2-methoxyphenyl)₂PCl (ligand composition L) was prepared as follows.

Under a nitrogen atmosphere, 3 ml triethylamine was added to 1.5 mlisopropylamine (17.6 mmol) in 5 ml dry toluene. To the resultingmixture, 2.2 g (7.84 mmol) (2-methoxyphenyl)₂PCl in 20 ml toluene wasslowly added and allowed to stir overnight at room temperature. Theprecipitate was removed by centrifugation. The solvents were removedfrom the resulting solution in vacuo. Washing with pentane yielded(2-methoxyphenyl)₂PNH(isopropyl) as a white solid. ³¹P-NMR (in C₆D₆) δ21.8.

Under a nitrogen atmosphere, 80 mg (1.0 mmol) of neopentyl lithium wasslowly added to 300 mg (0.99 mmol) of (2-methoxyphenyl)₂PNH(isopropyl)in 30 ml dry toluene. To the resulting mixture 277 mg (0.99 mmol)(2-methoxyphenyl)₂PCl was slowly added. The mixture was stirredovernight at room temperature. The precipitate was removed bycentrifugation. The solvent was removed in vacuo. The residue was washedwith pentane. The product has according to ³¹P-NMR at leastpredominantly the P—P═N(isopropyl) structure, i.e.(2-methoxyphenyl)₂P(2-methoxyphenyl)₂PN(isopropyl), and was used withoutfurther purification. ³¹P-NMR (in C₆D₆) δ 0.0 and −35.4 (J_(pp)=258 Hz).

Ligand Composition M″ (Comparative)

The (phenyl)₂PN(isopropyl)P(phenyl)₂ ligand was prepared by thefollowing method. At 0° C., under a nitrogen atmosphere, 15 mltriethylamine was added to 6.3 g (phenyl)₂PCl in 80 ml of drydichloromethane. To the resulting mixture, 0.844 g isopropylamine wasadded and allowed to stir overnight at room temperature. The solventswere removed from the resulting solution in-vacuo and 50 ml of drytoluene was added. The mixture was then filtered over a small layer ofsilica. The toluene was removed from the filtrate under vacuum,(phenyl)₂PN(isopropyl)P(phenyl)₂ product was isolated as a white solid.Crystallization from ethanol yielded (phenyl)₂PN(isopropyl)P(phenyl)₂ aswhite crystals.

Ligand Component N″ [Used in the In Situ Preparation of LigandComposition C′]

The (phenyl)₂PN(isopropyl)P(2-methoxyphenyl)₂ ligand was prepared by thefollowing method.

Under a nitrogen atmosphere, 12 ml triethylamine was added to 3.39 gisopropylamine in 10 ml dry toluene. To the resulting mixture, 5.15 ml(phenyl)₂PCl was slowly added and allowed to stir overnight at roomtemperature. The precipitate was removed by filtration. The solventswere removed from the resulting solution in vacuo. To the evaporationresidue pentane was added and subsequently the solvent was removed invacuo from the pentane solution, yielding (phenyl)₂PNH(isopropyl) as acolourless oil, which crystallized on standing at room temperature.

Under a nitrogen atmosphere, 3 ml triethyl amine was added to 0.9 g ofthe isolated (phenyl)₂PNH(isopropyl) in 5 ml of dry dichloromethane. Tothe resulting mixture, 1.1 g (2-methoxyphenyl)₂PCl was added and allowedto stir for a week at room temperature. To the resulting reactionmixture 5-10 ml of dry toluene was added. The precipitate was removed bycentrifugation. The solvents were removed from the resulting solution invacuo. The resulting mixture was first washed with pentane and thereuponstirred with methanol yielding a white solid. The white solid was washedwith pentane and dried in vacuo. Yield 0.7 g of(phenyl)₂PN(isopropyl)P(2-methoxyphenyl)₂. ³¹P-NMR (in C₆D₆) broadsignals δ 55.9 and 24.8.

Ligand Component Q [Used in the In Situ Preparation of LigandComposition T′]

The racemic phosphorus derivative of rac-2,2′dihydroxy-1,1′-binaphthyl,(Rac-1,1′-binaphthyl-2,2′-dioxy)PCl, also called(rac-1,1′-binaphthalene-2,2′-dioxy)PCl,rac-1,1′-binaphthyl-2,2′phosphorochloridite or(rac-O,O-binaphtholato)PCl was prepared from phosphorus trichloride andrac-2,2′-dihydroxy-1,1′-binaphthyl (purchased from Aldrich) according tothe method reported by N. Greene and T. P. Kee, Synthetic Communications23 (1993) 1651. The product showed in ³¹P-NMR (in C₆D₆) a signal at δ179.5 (δ_(P) 178.8 (s) according to the above-mentioned literature).

Ligand Composition T′

The reaction product of (2-methoxyphenyl)₂PN(methyl)P(2-methoxyphenyl)₂and (rac-1,1′-binaphthyl-2,2′-dioxy)PCl (ligand composition T′) wasprepared as follows.

In a NMR-tube under a nitrogen atmosphere 14 mg (40 mmol)(rac-1,1′-binaphthyl-2,2′-dioxy)PCl was added to 22 mg (36 mmol)(2-methoxyphenyl)₂PN(methyl)P(2-methoxyphenyl)₂ in 1 ml dry d8-toluene.This mixture was heated in an oil bath of 110° C. for 40 hours.According to ³¹P-NMR spectroscopy, the product was an approximately 1 to1 (mol/mol) mixture of (2-methoxyphenyl)₂PCl and predominantly aP—P═N(methyl) structure with on one P atom therac-1,1′-binaphthyl-2,2′-dioxy group and on the other P atom two2-methoxyphenyl groups (either(rac-1,1′-binaphthyl-2,2′-dioxy)P(2-methoxyphenyl)₂PN(methyl) or(2-methoxyphenyl)₂P(rac-1,1′-binaphthyl-2,2′-dioxy)PN(methyl)) (seeScheme 1). ³¹P-NMR (in C₇D₈) δ 151.3 and 35.1 (J_(pp)=385 Hz). Thismixture was used as such in the catalyst for ethylene oligomerizationexperiments without further purification.

Ligand Component U

The preparation of N-methylnaphto[1,8-de][1,3,2]dioxaphosphinine-2-amine(see Scheme 2).

Under a nitrogen atmosphere, 0.4 ml triethylamine was added to 1.5 mlmethylamine (2 M in THF) in 20 ml dry toluene. To the resulting solutionwas cooled to 5° C. and 250 mg2-chloronaphtho[1,8-de][1,3,2]dioxaphosphinine (available from HansaFine Chemicals GmbH, Bremen, Germany) was slowly added. After stirringovernight at room temperature 20 ml hexane was added. The precipitatewas removed by centrifugation. The solvents were removed under vacuum.The product N-methylnaphtho[1,8-de][1,3,2]dioxaphosphinine-2-amine wasisolated as an oil and used as such. ³¹P-NMR C₆D₆ δ 121.2.

Ligand Composition V

The reaction product ofN-methylnaphtho[1,8-de][1,3,2]dioxaphosphinine-2-amine and(2-methoxyphenyl)₂PCl (ligand composition V, see Scheme 3) was preparedas follows.

Under a nitrogen atmosphere, 350 mg triethylamine was added to 150 mgN-methylnaphtho[1,8-de][1,3,2]dioxaphosphinine-2-amine 20 ml drytoluene. To the resulting solution, 230 mg (2-methoxyphenyl)₂PCl wasslowly added and allowed to stir overnight at room temperature. To theresulting mixture hexane was added. The precipitate was removed bycentrifugation. The solvents were removed under vacuum. The product wascrystallized from a hexane/toluene mixture (−20° C.) and isolated as awhite solid. ³¹P-NMR C₆D₆ δ 130.6 and 36.3 (J_(pp)=370 Hz).

Co-Catalyst

The co-catalyst used in the experiments below was selected from:

Methyl aluminoxane (MAO) in toluene, [Al]=5.20% wt, supplied by CromptonGmbH, Bergkamen, Germany;

Examples 1-31 Catalyst System Preparation for Simultaneous Trimerizationand Tetramerization in a Batch Autoclave

In a Braun MB 200-G dry box the chromium tris(acetylacetonate)(typically about 30 μmol) and the ligand component, as indicated inTable 1, were placed in a glass bottle. Dry toluene (typically 4 g) wasadded to the glass bottle to obtain a catalyst precursor solution.Finally, the bottle was sealed by a septum cap.

The solution or part of the solution was used in the oligomerisationreaction of ethylene.

Oligomerisation Reactions of Ethylene in a 1.0-Liter Batch Autoclave

Oligomerisation experiments were performed in a 1.0-liter steelautoclave equipped with jacket cooling with a heating/cooling bath (ex.Julabo, model ATS-2) and a turbine/gas stirrer and baffles.

The reactor was scavenged by introducing 250 ml toluene, MAO (0.6 gsolution) and subsequent stirring at 70° C. under nitrogen pressure of0.4-0.5 MPa for 30 min. The reactor contents were discharged via a tapin the base of the autoclave. The reactor was evacuated to about 0.4 kPaand loaded with approximately 250 ml toluene, heated to 40° C. andpressurised with ethylene to 15 barg.

Whilst stirring, an MAO-solution (typically an intake of 3.12 g, 6 mmolAl, to attain an Al/Cr atomic ratio of 200) was added to the reactorwith the aid of toluene (the total volume injected was about 25 ml: theMAO-solution diluted with toluene to 8 ml was injected and the injectorsystem was rinsed twice with 8 ml toluene) and the stirring at 800 rpmwas continued for 30 minutes.

The Cr-catalyst precursor, prepared as described above, was introducedinto the stirred reactor using an injection system with the aid oftoluene (the total volume injected was about 25 ml: the catalystsolution diluted with toluene to 8 ml was injected and the injectorsystem was rinsed twice with 8 ml toluene). The initial loading of thereactor was about 300 ml of largely toluene.

The addition of the catalyst system resulted, after an initial inductionperiod of about 5 minutes, in an exotherm (generally 5-10° C.), whichtypically reached a maximum within 1 minute and was followed byestablishment of the temperature and pressure indicated in Table 1.

After consuming the desired volume of ethylene, the reaction was stoppedby rapid cooling to room temperature (about 5 minutes), followed byventing of the ethylene, and decanting the product mixture into acollection bottle using a tap in the base of the autoclave. Exposure ofthe mixture to air resulted in rapid deactivation of the catalyst.

After addition of n-hexylbenzene, (0.5-3.5 g) as an internal standard,to the crude product, the amount of the C₄-C₃₀ olefins and purity of C₆,C₈ and C₁₀ olefins was determined by gas chromatography. Theexperimental data is reported in Table 1.

In the case of experiments under 30, 40 or 50 barg of ethylene pressure,a similarly equipped 0.5-liter steel autoclave has been used, loaded (inthe same manner as the above-described procedure for the 1.0-literautoclave) with half the amounts of the components used in thecorresponding 1.0-liter experiments to maintain the same Al/Cr atomicratio (of about 200) and final alpha olefin concentration as much aspracticable.

The experimental data is provided in Table 1 below.

TABLE 1 The performance of R^(a) ₂P—P(R^(c))₂═N—R^(b),R^(b)—N═P(R^(a))₂PR^(c) ₂ and/or R^(a) ₂P—N(R^(b))—PR^(c) ₂ ligands inCr-catalyzed ethylene oligomerization Temperature Ligand (Initial Cr(mol_(lig)) Co- Temp) Pressure Time TOF C₆ Example (μmol) (mol_(Cr))Catalyst ( C.) (barg) (min) (TON) ^(‡) (% wt)  1 32 A MAO 70 15 30 13053.6 (1.1) (40)  (65)  2 15 A MAO 70 30 72 246 49.6 (1.1) (40) (295)  314 A MAO 85 30 35 415 51.1 (1.1) (40) (242)  4 15 A MAO 85 30 40 34350.6 (2.3) (40) (229)  5  3 A MAO 100  50 60 594 50.1 (1.1) (40) (594) 6  3 A MAO 100  50 90 365 52.4 (2.3) (40) (547)  7 30 A′ MAO 70 15   60##  76 45.1 (1.1) (40)  (76)  8 15 A′ MAO 70 30 38 139 33.4 (1.2) (70) (88)  9 20 A′ MAO 85 30 43  69 45.3 (1.2) (70)  (49) 10 30 B′ MAO 70 15  225 ##  20 57.2 (1.1) (40)  (76) 11 15 B′ MAO 70 30 94  48 45.5 (1.1)(70)  (75) 12 15 C″ MAO 70 30 19 317 50.8 (1.1) (70) (100) 13 15 C″ MAO85 30 80 185 59.8 (2.4) (40) (246) 14  3 C″ MAO 100  50 80 643 64.9(2.4) (40) (858)   15 # 15 D″ MAO 70 30 30  7 29.6 (1.3) (40)  (4) 16 15E MAO 70 30 30  9 10.6 (1.1) (40)  (4) 17 30 F MAO 70 15 85  78 38.8(1.1) (40) (111) 18 15 F MAO 70 30 37 270 44.7 (1.1) (40) (167) 19 16 FMAO 85 30 35 269 33.6 (2.3) (40) (157) 20  3 F MAO 100  50 60 181 40.8(2.3) (40) (181) 21 15 G″ MAO 70 30 35  5 58.9 (1.3) (70)  (3) 22 17 G″MAO 120  50 85  5 16.0 (2.4) (40)  (8)   23 # 15 H″ MAO 70 30 75  2 26.4(0.9) (40)  (3)   24 # 15 K″ MAO 70 30 36 705 85.0 (1.1) (40) (423)   25# 16 L MAO 70 30 20  5 82.5 (1.5) (70)  (2)   26 # 15 M″ MAO 40 30 33203 17.4 (1.1) (40) (113)   27 # 15 M″ MAO 80 30 30  26 20.3 (1.1) (80) (13) 28 15 T′ MAO 70 30 32 148 42.5 (1.1) (70)  (79) 29 15 T′ MAO 85 3037 137 49.2 (1.1) (85)  (84) 30 15 T′ MAO 85 40 30 183 44.0 (1.1) (85) (92) 31 15 V MAO 70 30 21 174 32.5 (1.2) (70)  (61) 1-C₆ + 1-C₈ onTotal Total 1-C₆* C₈ 1-C₈** C₁₀ ^(†) C₁₂-C₁₄ ^(†) Solids Product ProductExample (% wt) (% wt) (% wt) (% wt) (% wt) (% wt) (g) (% wt)  1 97.735.9 98.4 3.4 4.6 0.05 54.6 87.7  2 97.7 38.2 98.5 4.1 4.6 0.02 124.386.1  3 97.4 37.2 98.3 3.6 4.4 1.5 95.8 86.4  4 97.4 38.5 98.3 3.4 4.41.0 96.1 87.2  5 97.6 32.2 98.3 2.9 2.4 10.3 49.8 80.5  6 97.4 38.5 98.32.6 2.8 1.4 45.7 88.9  7 97.2 44.6 98.5 2.4 4.4 0.05 64.8 87.8  8 96.752.7 98.5 2.0 4.4 1.3 37.2 84.1  9 97.1 43.1 98.2 2.1 3.4 1.7 28.1 86.310 94.1 31.7 97.2 4.3 4.3 0.08 62.8 84.6 11 92.0 43.6 96.8 3.5 4.6 0.531.5 84.1 12 98.6 34.2 98.8 8.1 6.8 0.07 43.5 83.8 13 98.2 22.6 98.410.3  5.7 0.6 103.1 81.0 14 98.1 21.1 98.3 8.6 3.9 1.0 71.6 84.3   15 #71.6 60.8 97.1 2.1 2.2 2.7 1.5 80.2 16 66.4 21.6 92.6   5.5 †† 7.5 43.41.8 27.0 17 98.8 25.7 99.2 5.4 5.5 19.3 93.4 63.9 18 99.0 39.0 99.5 5.26.0 3.7 69.8 83.0 19 98.7 24.9 99.2 3.7 4.7 25.0 70.0 57.9 20 98.8 26.899.3 3.0 3.5 19.7 15.2 66.9 21 97.8 12.4 95.5 4.5 4.5 18.6 1.2 69.4 2295.8 4.7 91.8 2.1 2.9 65.1 3.6 19.6   23 # 93.6 24.6 96.1  10.9 †† 14.37.7 1.3 48.3   24 # 97.5 4.1 99.8 10.0  0.9 0.02 177.6 87.0   25 # 100.03.6 93.0 3.0 3.1 7.2 0.7 85.8   26 # 68.5 70.2 98.8   1.8 †† 4.4 0.547.2 81.3   27 # 92.8 25.9 94.4   2.3 †† 3.7 47.4 5.5 43.3 28 97.6 48.398.6 1.9 3.1 0.06 33.9 89.1 29 97.3 43.8 98.4 2.1 2.8 0.06 35.2 90.9 3097.1 47.8 98.5 1.9 2.9 0.05 38.7 89.8 31 96.5 53.8 98.6 1.8 3.4 3.5 25.484.4 The following equilibria are assumed in the presence of activatedchromium: R^(a) ₂P—P(R^(c))₂═N—R^(b) 

 R^(a) ₂P—N(R^(b))—PR^(c) ₂

 R^(b)—N═P(R^(a))₂—PR^(c) ₂ A R^(a) ₂ = o-phenylenedioxy, R^(b) =methyl, R^(c) = o-methoxyphenyl (A: ligand predominantly in either ofthe P—P═N forms). A′ R^(a) ₂ = o-phenylenedioxy, R^(b) = methyl, R^(c) =o-methoxyphenyl (A′: in-situ prepared ligand A; containing about 1mol/mol (o-methoxyphenyl)₂P—Cl). B′ R^(a) ₂ = o-phenylenedioxy, R^(b) =methyl, R^(c) ₂ = o-methylphenyl + phenyl (B′: in-situ prepared ligandB, predominantly in either of the P—P═N forms; containing about 1mol/mol (o-methoxyphenyl)(phenyl)P—Cl). C″ R^(a) ₂ = o-phenylenedioxy,R^(b) = isopropyl, R^(c) = o-methoxyphenyl (C″: ligand predominantly inthe P—N—P form). D″ R^(a) ₂ = o-phenylenedioxy, R^(b) = isopropyl, R^(c)= phenyl (D″: ligand predominantly in the P—N—P form). E R^(a) ₂ =o-phenylenedioxy, R^(b) = methyl, R^(c) = phenyl (E: ligandpredominantly in either of the P—P═N forms). F R^(a) ₂ =o-phenylenedioxy, R^(b) = methyl, R^(c) = tert-butyl (F: ligandpredominantly in either of the P—P═N forms). G″ R^(a) ₂ =o-phenylenedioxy, R^(b) = pentafluorophenyl, R^(c) = o-methoxyphenyl(G″: ligand predominantly in the P—N—P form). H″ R^(a) ₂ =o-phenylenedioxy, R^(b) = methyl, R^(c) ₂ = o-phenylenedioxy (H″: ligandpredominantly in the P—N—P form). K″ R^(a) = o-methoxyphenyl, R^(b) =methyl, R^(c) = o-methoxyphenyl (K″: ligand predominantly in the P—N—Pform). L R^(a) = o-methoxyphenyl, R^(b) = isopropyl, R^(c) =o-methoxyphenyl (L: ligand predominantly in either of the P—P═N forms).M″ R^(a) = phenyl, R^(b) = isopropyl, R^(c) = phenyl (M″: ligandpredominantly in the P—N—P form). T′ R^(a) ₂ =rac-1,1′-binaphthyl-2,2′-dioxy, R^(b) = methyl, R^(c) = o-methoxyphenyl(T′: in-situ prepared T, predominantly in either of the P—P═N forms;containing about 1 mol/mol (o-methoxyphenyl)₂P—Cl). V R^(a) ₂ =1,8-naphthalenedioxy, R^(b) = methyl, R^(c) = o-methoxyphenyl (V: ligandpredominantly in either of the P—P═N forms). # Comparative example. ##During 30 minutes at 40° C. ^(‡) Turnover frequency (TOF) in hourly kmolconverted ethylene/mol catalyst (kmol/mol*h); turnover number (TON) inkmol converted ethylene/mol catalyst (kmol/mol). *Percentage (%) of1-hexene by weight of the C₆ portion of the product composition.**Percentage (%) of 1-octene by weight of the C₆ portion of the productcomposition. ^(†)Predominantly branched and/or internal olefins, unlessindicated differently. †† Equal or larger than 50% of 1-decene by weightof the C₁₀ portion of the product composition. C₆ Hydrocarbonscontaining 6 carbon atoms; 1-C₆ is 1-hexene. C₈ Hydrocarbons containing8 carbon atoms; 1-C₈ is 1-octene. C₁₀ Hydrocarbons containing 10 carbonatoms. C₁₂-C₁₄ Hydrocarbons containing 12 and/or 14 carbon atoms.Solids: The amount of wax and polyethylene isolated by filtration. Totalproduct: The amount of C₄-C₁₀₀ olefins, derived from GC analysis,including the amount of solids.

For economic narrow-cut alpha-olefin production, e.g. the production ofa mixture of 1-hexene and 1-octene in a combined overall yield of >80%,preferably in a weight ratio of 20/80 to 80/20, each in >92% selectivity(on total C6 or total C8) in a single plant to enhance the economy ofscale a special kind of catalyst is required. At industriallyinteresting pressures and temperatures of at least 30 barg and 70° C.the comparative catalyst K″ and analogous catalyst L predominantlyproduce 1-hexene and hardly 1-octene. Under these conditions thecomparative catalyst M″ produces a mixture of hexenes and octenes of low1-hexene content, but also a large amount of solids at a low TOF. Onlyat 40° C. comparative catalyst M″ produces a mixture of hexenes andoctenes of low 1-hexene content at a high TOF.

Surprisingly only the “o-phenylenedioxy-phosphorus” containing catalystsA, A′, C″, the rac-1,1′-binaphthyl-2,2′-dioxy-phosphorus containingcatalyst T′ and the 1,8-naphthalenedioxy-phosphorus containing catalystV and to a less extent B′ and F, but remarkably to far less extent, ifany, D″, E, G″, and H″, produce mainly 1-hexene and 1-octene in highactivities (TOF's) at temperatures of 70° C. and 30 barg. Even at70-100° C. and 30-50 barg catalysts A, A′, C″ and T′ provide for theselective production of both highly pure 1-hexene and 1-octene in thedesired weight ratios with only minor amounts of solids (wax andpolyethylene) co-produced. Hence, what is particularly preferred forefficient narrow-cut production of highly pure 1-hexene and 1-octene atindustrially interesting rates and temperatures and pressures is aCr-complex with a PNP structure or its PPN isomers with a methyl orisopropyl group on N, one cyclic alkylenedioxy or arylenedioxy group,preferably one—optionally mono-tetra alkylated—o-phenylenedioxy(catechol) or one—optionally mono-dodeca alkylated—racemic or opticallypure 1,1′-binaphthyl-2,2′-dioxy group on one P and at least oneo-methoxyphenyl and one phenyl, but preferably two o-methoxyphenylgroups on the other P. If, instead two tert-butyl (also stericallydemanding, but electronically different) groups are present on thelatter P, generally besides 1-hexene and 1-octene a relatively large(>3.7% wt) amount of solids, mainly wax, is co-produced.

It should be noted that the differences in hexenes/octenes ratiosbetween experiments with ligand A and in-situ prepared ligand A (ligandA′) are probably due to the differences in start-up temperature. Theactivities obtained with the in-situ prepared ligand A′ are howeverinvariably lower than those obtained with ligand A, which is ascribed tothe presence of (o-methoxyphenyl)₂P—Cl.

The invention claimed is:
 1. A catalyst system comprising: a) a sourceof chromium, molybdenum or tungsten; b) a ligand having the generalformula (VI):(R⁹)(R¹⁰)P—N(R³)—P(R⁴)  (VI) wherein: the R⁹ and R¹⁰ groups areindependently selected from optionally substituted alkyl or heteroalkylgroups; the R³ group is selected from hydrogen, a hydrocarbyl group, asubstituted hydrocarbyl group, a heterohydrocarbyl group, a substitutedheterohydrocarbyl group, or a silyl group; the R⁴ group is an optionallysubstituted alkylenedioxy or alkylenedimercapto structure which is boundto the phosphorus atom through the two oxygen or sulphur atoms of thealkylenedioxy or alkylenedimercapto structure or an optionallysubstituted arylenedioxy or arylenedimercapto structure which is boundto the phosphorus atom through the two oxygen or sulphur atoms of thearylenedioxy or arylenedimercapto structure.
 2. The catalyst systemaccording to claim 1, wherein the R⁴ group is an optionally substitutedalkylenedioxy structure which is bound to the phosphorus atom throughthe two oxygen atoms of the alkylenedioxy structure or an optionallysubstituted arylenedioxy which is bound to the phosphorus atom throughthe two oxygen atoms of the arylenedioxy structure.
 3. The catalystsystem according to claim 1, wherein the R⁴ group is an optionallysubstituted 1,2-arylenedioxy group having the following structure:

which is bound to the phosphorus atom through the two ortho positionedoxygen atoms of the ortho-arylenedioxy structure, and wherein the R¹¹ toR¹⁴ groups on the phenyl ring are independently selected from hydrogen,hydrocarbyl groups, substituted hydrocarbyl groups, or any two of theR¹¹ to R¹⁴ groups are linked together to form a cyclic hydrocarbyl orheterohydrocarbyl structure.
 4. A process for the oligomerisation ofolefinic monomers, wherein the process comprises contacting at least oneolefinic monomer with the catalyst system of claim 1.